bingo, that is it - at least in my case;-)
couple of days ago i experienced some oddities in my sidebar too. some icons in the sidebar (and that is the odditie) changed their userdefined appearence into the generic icon again, - randomly, it seemed. While others kept their icon steady.
I moved the generic one from the sidebar and dragged the file (with userdefined icon) over to the sidebar again. Pleasure was short, split second later, the icon changed into generic one again. Same procedere over and over. It gaves me the creeps.
All at a sudden i learned: it only happend to sidebar-icons which windows/direct. were wide open AND files gonna moved inside or outside that particular window/direct. And the bottom line is: sidebar icons can loose their (userdefined) appearence while work is in progress;-)
well, perhaps that helps.
btw, repairing permissions is good from time to time, cleaning cache is much, much better. MacosX seems to be lousy (or should i say loosy?) when it comes to cachefiles. it likes to bust them, somehow ... imho.
bust ... er ... best