I'm not really convinced that zapping the mailbox is going to fix a pending icon problem. Usually those are either communications problems between client/server, or evidence of a more complex problem (aka dcom/http). Of course, if your safety copy setting isn't set to your liking, then you'll get this behavior as well (in which case it's normal). So do check that before you start debugging.
So instead of zapping, do a cancel operation on all active pending items in the mailbox. Then launch the client side tools, select the maximum level of logging, and also run a dtrace on the EV server which is running the archive task/hosting the vault. Then try a manual archive and see where it falls down.
micah