Unity-Technologies/mono — pull request #70 by Tak (2013-06-07 08:27:08+00:00)
Title: Don't assert when trying to re-expand a template. See case #542749

In some very specific situation where there's classes that inherit
from a generic base class like:

BaseClass : MonoBehaviour where T : BaseClass
AClass : BaseClass

the compiler tries to expand the templates twice. *boggle*