1) dockstar; mailfollowup
2) 10.6.1
3) not sure, will report back if i end up testing
4) shortly after updating to 10.6.1; never happened in leopard, and i don't think it happened in 10.6.0
5) i tried mailbox->rebuild messages, which seemed to have helped once, but the problem came back; trashing both mail's and the dock's plists didn't help either. in a possibly related issue, mail occasionally crashes my dock, i.e., my auto-hide dock fails to appear, and cmd-tab stops working.