After recently upgrading to 1.2b1, I noticed this bug.
In the inheritance-diagram extension, it now uses the first line of the docstring as tooltips. However, if that first line contains a quote, it is not escaped, and therefore the generated dot file has syntax errors.
This pull request represents the simplest possible way to fix this, but it may in fact be better to update the graphviz extension so that is performs escaping on all strings that are output. If you'd rather do that, let me know, and I can probably whip something up.