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.

Weirdly enough someone reported a Ubuntu bug I had and I was able to just respond to the email chain with more useful information as to the cause and that was that. I think mailing lists are powerful they just need to be clearer on how to use them and have some tutorial links towards the bottom. Dont ask me how you start a new email chain for a new bug though. I wouldn't know. To be fair I dont remember how I responded initially.

I agree though sometimes I dont bother reporting bugs if its not on GitHub or a system I am already registered for.