I agree. Simply stating "this is a known bug, here's the bug report" is a pretty crappy answer. If that's all the answer that can be given, it would be better to just close the question as a bug report. That's one of the boilerplate close reasons available on Ask Ubuntu:
If, on the other hand, there is useful information in the bug report. Then, instead of just linking, copy the information into your answer as the OP of your example did.
So yes, in my opinion, an answer that's just a link to a bug report is useless. It is not an answer as defined by SE, and it would be better to post it as a comment and close the question.
