The bug report is at https://bugs.launchpad.net/ubuntu/+source/tidy/+bug/589574 with a test case against an old version of libtidy. The diagnosis is "use after free". Suggestions: - [x] replicate the bug on current distributions - [ ] add test case to tests - [x] show that the bug has been fixed in tidy-html5 - [x] recommend that Ubuntu pick up tidy-html5 to replace the old libtidy.