When storing a ctype function pointer in a ctype structure field, a reference remains even when that field is overwritten with some values:
- None
- None cast into a function pointer
But the reference is somehow removed when overwriting the field with a "real" function pointer (a lambda in attached test case).

This causes problem when the structure is a class property and function pointer is created out of a method of the same class: a circular reference is created, which is not garbage-collected.

To run the attached test case, you need objgraph[1], and to uncomment one (or none) of the commented-out lines in "close" method.

[1] http://mg.pov.lt/objgraph/