Help: Found odd git bug

Hi all,

A commit claims to add a line to a file.  Indeed, "git diff" shows the line
being added.

However, when I check out the commit, the file contains a *different* line,
with slightly modified contents.

What's more, "git show SHA:path/to/file" shows that the blob contains the
wrong line.

I found this using git 1.7.9, but 1.7.11.rc1 also shows the problem.

How can I narrow down what's causing this problem?

		M.