That's the intention.  Otherwise if you modified the keyword without renaming, the icon remained attached to any posts where it was selected with pic#xxx rather than dropping back to default.  It _does_ mean that if they subsequently modify the keyword back to pic#xxx then the icon won't reappear on the post.  We discussed this and in the end decided we should document the edge case rather than attempting to fix it.  Fu's asked if I can put a comment on Bugzilla about it, but I've not got around to it yet.  Should do in the next 24 hours or so.