ThreadOpenTkControl System.AccessViolationException

I'm using your control in combination with AvalonDock to use dockable Panes like with VisualStudio.
When undocking or docking the pane, sometimes a System.AccessViolationException happens.

GL.ReadPixels(0, 0, _bitmapWidth, _bitmapHeight, PixelFormat.Bgra, PixelType.UnsignedByte, _backBuffer);
_previousUpdateImageTask = RunOnUiThread(() => UpdateImage(dirtyArea));

[Exception Infos]
An unhandled exception of type 'System.AccessViolationException' occurred in OpenTK.dll
Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. occurred

OpenTkControl.AvalondockExample.zip