Mime-Type issue in HEAD?

MonoDevelop doesn't open any files no more (except solutions). This
startet after a svn update last week. The error I get is:

Error while loading System.InvalidCastException: Cannot cast from source
type to destination type.
in <0x00058>
GtkSourceView.SourceLanguagesManager:GetLanguageFromMimeType
(System.String mime_type)
in <0x00013>
MonoDevelop.Services.SourceViewService:GetLanguageFromMimeType
(System.String mimetype)
in <0x00016> MonoDevelop.SourceEditor.Gui.SourceEditorBuffer:LoadText
(System.String text, System.String mime)
in <0x00036> MonoDevelop.SourceEditor.Gui.SourceEditorBuffer:LoadFile
(System.String file, System.String mime)
in <0x00050>
MonoDevelop.SourceEditor.Gui.SourceEditorDisplayBindingWrapper:Load
(System.String fileName)
in <0x0002e>
MonoDevelop.SourceEditor.Gui.SourceEditorDisplayBinding:CreateContentForFile 
(System.String fileName)
in <0x00023> MonoDevelop.Services.DefaultFileService
+LoadFileWrapper:Invoke (System.String fileName)
in (wrapper delegate-invoke) System.MulticastDelegate:invoke_void_string
(string)
in <0x00014> MonoDevelop.Core.Services.FileUtilityService
+LoadWrapper:Invoke ()
in (wrapper delegate-invoke) System.MulticastDelegate:invoke_void ()
in <0x00018> MonoDevelop.Core.Services.FileUtilityService:ObservedLoad
(MonoDevelop.Core.Services.FileOperationDelegate saveFile, System.String
fileName, System.String message, FileErrorPolicy policy)

What could be the problem?

I'm using:
mono-1.1.6
gtk-sharp-1.9.3
gtksourceview-1.2
gtksourceview-sharp: svn HEAD