The problem I have seen is that certain usually vocal members of a community can have this double-edged helpful-jerk attitude. Most of the time I just lurk on communities, so the jerkiness is rarely if ever even directed at me, but it changes my view of the project to the point where I just don't want to be involved.
The usual pattern is a post or response to a bug report, patch or question that is generally helpful but at the same time needlessly nasty or snarky, and with a I-know-better-than-you attitude. If the community person dislikes the question asked, or the use that people make of their software, why do they take the time to write answers at all? Usually being pleasant is a question of writing less words as well. These people go out of their way to add snark to the response.
This isn't limited to "open source". It is probably just a people problem. I've seen the exact same thing on guitar forums. Members that post helpful replies, but spread a layer of snark over them. You follow their profile and they often have websites with lots of good free information, lessons and whatnot, but here they are, writing twatish answers. It has been a problem on stackoverflow.com too, and they really stirred things up over there recently trying to herd people into being a bit nicer.