Julian (http://somethinkodd.com/oddthinking) reports:
On my project, I put the test cases for foo.py in foo.test.py. I don't know why I do this; it is just what my predecessor did.
In this case, in the HTML index page, clicking on the foo.py line takes you to the foo.test.py coverage instead.
If I rename the test cases to foo_test.py, it functions perfectly, and is quite an eye-opener to the amount of code never executed.
(This bug-report can be filed under "If it hurts when you do that, then don't do that," but I thought I would let you know.)