See issue 104487 for one recent example. An issue was flagged up where HTML5 videos weren't playing properly when given a poster image but no controls attribute.

The issue was closed almost immediately, with some obviously hastily written comments, apparently because no-one could reproduce it in a different version of Chrome on Linux or Mac. As far as I can see, no-one even tried to reproduce the other reported failing case on Windows, and there was no attempt at all to investigate the original bug and determine how it happened and why it was no longer observable on the platforms tested.

The issue was simply marked "fixed", despite no actual fix having been identified, rather than giving it a more specific "no longer reproducible" status.

There are still serious problems with that combination of attributes today.