Brep.CreateEdgeSurface not Threadsafe?

I am developing a plugin with multiple components and run into a problem with Brep.CreateEdgeSurface in a thread.
( Brep sideSrf = Brep.CreateEdgeSurface(new Curve { topCurve, btmCurve }); )
Its throwing a System.AccessViolationException and completly crashes Rhino afterwards.

I am doing a lot of stuff before this, like Brep.CreatePlanarBreps and everything is working fine.

The used curves only exist in the Object that is created during the thread, so no other threads are accessing them.

So is Brep.CreateEdgeSurface not threadsafe? Is there any way to see which Brep functions are threadsafe?
Brep.CreateFromLoft e.g. seems again to be threadsafe.