In my usecase, I wanted to override the behaviour of __getitem__. I was able to accomplish this by subclassing EnumMeta. 

Having done so, I was able to work around this bug as follows. Instead of trying to access the functional API via Enum (using an enum as the type parameter) and failing, I was able to succeed by accessing the functional API via subclass of Enum. Something like:
MyEnum2 = MyEnumBase1(...)