In any project that’s making active use of its bug tracker, there is always a danger of the tracker turning into a discussion forum itself, even though the mailing lists would really be better. Usually it starts off innocently enough: someone annotates an issue with, say, a proposed solution, or a partial patch. Someone else sees this, realizes there are problems with the solution, and attaches another annotation pointing out the problems. The first person responds, again by appending to the issue…and so it goes.

The problem with this is, first, that the bug tracker is a pretty cumbersome place to have a discussion, and second, that other people may not be paying attention – after all, they expect development discussion to happen on the development mailing list, so that’s where they look for it. They may not be subscribed to the issue changes list at all, and even if they are, they may not follow it very closely.

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There isn’t one right answer, but there is a general principle: if you’re just adding data to an issue, then do it in the tracker, but if you’re starting a conversation, then do it on the mailing list. … To use a mathematical analogy, if the information looks like it will be quickly convergent, then put it directly in the bug tracker; if it looks like it will be divergent, then a mailing list or IRC channel would be a better place.

— Karl Fogel, Producing Open Source Software