As a general guideline in IMP get_ methods never returns a reference and so doing things like get_foo.begin() is never a safe thing. Any such method which happens to return a reference is just an optimization for efficiency and might change later.

The only way I know to nicely catch the problem that Keren encountered is to turn on iterator debugging in gcc, but that changes the C++ ABI and so is a bit awkward if you link against any other C++ libraries.