Whenever I've found any kind of bug in Xubuntu or Ubuntu I would just rise a question about how to fix that on askubuntu.com. If it was my fault rather than a bug the folks would help me, if it was a bug they would confirm that. Some times I would even post a question and answer it myself immediately in cases when I've found a problem and a way to fix/workaround it myself. This way I make sure I'm not the only to know about the bug, the bug and the fact somebody is affected is known to the public. I just hope Canonical engineers actually read the site occasionally.