/usr/share/apport/apport-gtk:11:visit_decref:dict_traverse:subtract_refs:collect:collect_with_callback

The Ubuntu Error Tracker has been receiving reports about a problem regarding apport. This problem was most recently seen with package version 2.20.7-0ubuntu3.7, the problem page at https://errors.ubuntu.com/problem/c0d8d8079dd85ddb7fc7f704224beaa7ee0ebcf1 contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.