diff --git a/src/Eto.DevExtension.LanguageServer/Eto.DevExtension.LanguageServer.csproj b/src/Eto.DevExtension.LanguageServer/Eto.DevExtension.LanguageServer.csproj
index 12b66aa..fe49ca9 100644
--- a/src/Eto.DevExtension.LanguageServer/Eto.DevExtension.LanguageServer.csproj
+++ b/src/Eto.DevExtension.LanguageServer/Eto.DevExtension.LanguageServer.csproj
@@ -24,11 +24,6 @@
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" />
   </ItemGroup>
 
-  <ItemGroup>
-    <!-- reads code behind to list and add event handlers -->
-    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" />
-  </ItemGroup>
-
   <ItemGroup>
     <!-- resolved at runtime from the user's project, so keep it out of the probing path -->
     <PackageReference Include="Eto.Forms" PrivateAssets="all" ExcludeAssets="runtime" GeneratePathProperty="true" />
diff --git a/src/Eto.DevExtension.VisualStudio.Windows/Editor/EtoPreviewPane.cs b/src/Eto.DevExtension.VisualStudio.Windows/Editor/EtoPreviewPane.cs
index 0c6c1f4..f265729 100644
--- a/src/Eto.DevExtension.VisualStudio.Windows/Editor/EtoPreviewPane.cs
+++ b/src/Eto.DevExtension.VisualStudio.Windows/Editor/EtoPreviewPane.cs
@@ -125,6 +125,7 @@ void RegisterIndependentView(bool subscribe)
 		public EtoPreviewPane(EtoAddinPackage package, string fileName, IVsTextLines textBuffer, string projectKey, CodeEditorHost codeEditor)
 			: base(package)
 		{
+			ThreadHelper.ThrowIfNotOnUIThread();
 			this.editor = codeEditor;
 			this.package = package;
 			this.textBuffer = textBuffer;
@@ -138,6 +139,7 @@ public EtoPreviewPane(EtoAddinPackage package, string fileName, IVsTextLines tex
 			host.ProjectChanged += PreviewHost_ProjectChanged;
 			var designHost = new RemoteDesignPanel(async request =>
 			{
+				await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();
 				var snapshot = documentBuffer?.CurrentSnapshot;
 				var result = await host.RenderAsync(request, await ProjectAssemblyPaths.GetAsync(fileName));
 				if (snapshot != null && !disposed)
@@ -163,7 +165,11 @@ public EtoPreviewPane(EtoAddinPackage package, string fileName, IVsTextLines tex
 			};
 			preview = previewSplitter.Preview;
 			PreviewLayoutSettings.Load(previewSplitter);
-			previewSplitter.LayoutChanged += (sender, e) => PreviewLayoutSettings.Save(previewSplitter);
+			previewSplitter.LayoutChanged += (sender, e) =>
+			{
+				ThreadHelper.ThrowIfNotOnUIThread();
+				PreviewLayoutSettings.Save(previewSplitter);
+			};
 
 			platformDropDown = new DropDown { ToolTip = "Platform to draw the preview with" };
 			platformDropDown.SelectedKeyChanged += PlatformDropDown_SelectedKeyChanged;
@@ -307,7 +313,7 @@ protected override void Initialize()
 
 			// the document may not be registered yet while the frame is being created
 			if (!LockDocument())
-				ThreadHelper.JoinableTaskFactory.StartOnIdle(() => LockDocument());
+				_ = ThreadHelper.JoinableTaskFactory.StartOnIdle(() => LockDocument());
 
 			preview.Update();
 		}
@@ -581,7 +587,11 @@ public override int LoadUIState(Stream stateStream)
 		public int GetViewClassID(out Guid pclsidView) => editor.codeWindow.GetViewClassID(out pclsidView);
 		public int SetBaseEditorCaption(string[] pszBaseEditorCaption) => editor.codeWindow.SetBaseEditorCaption(pszBaseEditorCaption);
 		public int GetEditorCaption(READONLYSTATUS dwReadOnly, out string pbstrEditorCaption) => editor.codeWindow.GetEditorCaption(dwReadOnly, out pbstrEditorCaption);
-		public int Close() => editor.Close();
+		public int Close()
+		{
+			ThreadHelper.ThrowIfNotOnUIThread();
+			return editor.Close();
+		}
 		public int GetLastActiveView(out IVsTextView ppView) => editor.codeWindow.GetLastActiveView(out ppView);
 
 		int IVsCodeWindowEx.Initialize(uint grfCodeWindowBehaviorFlags, VSUSERCONTEXTATTRIBUTEUSAGE usageAuxUserContext, string szNameAuxUserContext, string szValueAuxUserContext, uint InitViewFlags, INITVIEW[] pInitView) => ((IVsCodeWindowEx)editor.codeWindow).Initialize(grfCodeWindowBehaviorFlags, usageAuxUserContext, szNameAuxUserContext, szValueAuxUserContext, InitViewFlags, pInitView);
diff --git a/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewHostClient.cs b/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewHostClient.cs
index 982f158..bf852ba 100644
--- a/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewHostClient.cs
+++ b/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewHostClient.cs
@@ -1,5 +1,6 @@
 using Eto.Designer;
 using Eto.Drawing;
+using Microsoft.VisualStudio.Shell;
 using Newtonsoft.Json.Linq;
 using StreamJsonRpc;
 using System;
@@ -71,6 +72,8 @@ public async Task<PreviewRenderResult> RenderAsync(PreviewRenderRequest request,
 			await requestLock.WaitAsync();
 			try
 			{
+				// the platform and theme choices are read from VS settings
+				await ThreadHelper.JoinableTaskFactory.SwitchToMainThreadAsync();
 				// a second try covers a host that exited after a rebuild, or that serves an older build
 				var wanted = await PreviewPlatforms.ResolveAsync();
 				var theme = PreviewPlatforms.ThemeChoice;
diff --git a/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewPlatforms.cs b/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewPlatforms.cs
index 96a4dd4..0e1bedc 100644
--- a/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewPlatforms.cs
+++ b/src/Eto.DevExtension.VisualStudio.Windows/Editor/PreviewPlatforms.cs
@@ -86,9 +86,14 @@ public static List<PreviewPlatform> GetAvailable()
 		/// <summary>A platform id or <see cref="Auto"/>, remembered for each solution. Use on the UI thread.</summary>
 		public static string Choice
 		{
-			get => GetChoice(CollectionPath, Auto, unsavedChoice);
+			get
+			{
+				ThreadHelper.ThrowIfNotOnUIThread();
+				return GetChoice(CollectionPath, Auto, unsavedChoice);
+			}
 			set
 			{
+				ThreadHelper.ThrowIfNotOnUIThread();
 				if (SetChoice(CollectionPath, value ?? Auto, Auto, ref unsavedChoice))
 					ChoiceChanged?.Invoke(null, EventArgs.Empty);
 			}
@@ -97,9 +102,14 @@ public static string Choice
 		/// <summary>A theme name from the host, or <see cref="DefaultTheme"/>, remembered for each solution. Use on the UI thread.</summary>
 		public static string ThemeChoice
 		{
-			get => GetChoice(ThemeCollectionPath, DefaultTheme, unsavedTheme);
+			get
+			{
+				ThreadHelper.ThrowIfNotOnUIThread();
+				return GetChoice(ThemeCollectionPath, DefaultTheme, unsavedTheme);
+			}
 			set
 			{
+				ThreadHelper.ThrowIfNotOnUIThread();
 				if (SetChoice(ThemeCollectionPath, value ?? DefaultTheme, DefaultTheme, ref unsavedTheme))
 					ThemeChoiceChanged?.Invoke(null, EventArgs.Empty);
 			}
diff --git a/src/Eto.DevExtension.VisualStudio.Windows/Wizards/WindowTitleBar.cs b/src/Eto.DevExtension.VisualStudio.Windows/Wizards/WindowTitleBar.cs
index a9f169e..6c11cac 100644
--- a/src/Eto.DevExtension.VisualStudio.Windows/Wizards/WindowTitleBar.cs
+++ b/src/Eto.DevExtension.VisualStudio.Windows/Wizards/WindowTitleBar.cs
@@ -1,4 +1,6 @@
 using Microsoft.VisualStudio.PlatformUI;
+using Microsoft.VisualStudio.Shell;
+using Microsoft.VisualStudio.Threading;
 using System;
 using System.Runtime.InteropServices;
 using System.Windows;
@@ -23,7 +25,16 @@ static class WindowTitleBar
 		public static void Attach(Window window)
 		{
 			void Apply() => ApplyTheme(window);
-			void ThemeChanged(ThemeChangedEventArgs e) => window.Dispatcher.BeginInvoke((Action)Apply);
+			void ThemeChanged(ThemeChangedEventArgs e)
+			{
+				// may be raised off the UI thread
+				var factory = EtoAddinPackage.Instance?.JoinableTaskFactory ?? ThreadHelper.JoinableTaskFactory;
+				factory.RunAsync(async () =>
+				{
+					await factory.SwitchToMainThreadAsync();
+					Apply();
+				}).Task.Forget();
+			}
 
 			if (new WindowInteropHelper(window).Handle != IntPtr.Zero)
 				Apply();