Coverage.py, version 3.5.3
Python 3.3.0 (v3.3.0:bd8afb90ebf2, Sep 29 2012, 01:25:11)
OS X 10.8
I have reproduced a situation where coverage erroneously reports a line as only being partially covered.
Please see the attache 'test.py' which you can use to duplicate the problem. The comments inside of test.py also discuss the issue in more depth.