Sounds like a bug, if it doesn't.
Patches welcome---I suspect that it can be solved the same way as
the recent cherry-pick patch by Miklos.
It's not as pressing as the glaring Documentation inaccuracies, so
I'll queue the task.
To exclude this case, I would say the most technically accurate
description of what 'git log' takes is a "committish range" (basically
a "revision range" that resolves to commits).