1) moving of the thread to the bin causes an email update - that's bad. You don't want watchers emailed for this reason.
No, that's not the case - moving a topic doesn't cause an email to be sent.
2) thread in the bin being updated alerts watchers who can't view the bin - that's bad. We're being told about things we can't access.
That was the case until today's deployment. But now, if a topic in the Trash is updated, only those folks who can access it are notified (meaning JavaRanch moderators).
3) delayed access. Thread is in real world at 12pm. Update happens at 1pm triggering email. 2pm thread moved to bin. 3pm I check mail and try to access and am told my privilges aren't in order.
That's still an issue, but I'm not sure it's worth addressing. The message is essentially correct, although not very satisfactory. But not that many topics are trashed, so I think this is acceptable.