I want to point you to this bug:
Do you see the Won’t Fix there?
Let us take a look at what ExecutionEngineException is all about, okay?
Now, the real problem here is that along with this issue there is a failing sample, so it is not a case of not being able to reproduce the error. Granted, the customer has managed to find a workaround for their problem, but the bug in the framework is still there, and was not fixed. I would assume that CLR crashing bugs that “should never occur” would be given some priority, even if the customer managed to find a workaround.