It seems the dictionaries used in the context class have some thread racing occurring when you have multiple WPF render threads (with own dispatchers). Some locks should fix it.
Comments: ** Comment from web user: RaceRalph **
Comments: ** Comment from web user: RaceRalph **
This has already been discussed [HERE](https://writeablebitmapex.codeplex.com/workitem/20005). It seems just replacing Dictionary with ConcurrentDictionary helps. In my project I haven't noticed any performance penalty introduced by this change (I have used a profiler).