I ran across a odd bug the other day. Essentially, when M-q is run with an open bracket in python mode, emacs will freeze.
To replicate the error:
$ emacs test.py
then hit M-q
The version of emacs I'm using is:
GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.7)
of 2014-03-07 on lamiak, modified by Debian
Its not a huge deal, it just struck me as odd since it generally really difficult to get emacs to crash.