Hi Perry,
Thanks for your reply(ies).
I'm not sure why this mirror failed to switch roles & back. But I've learned a few things along the way:
1) as soon as you break the mirror, checkpoint takes care of the the extra backed up tran log records so (b) above was unnecessary.
2) my mirror became 'orphaned' after I broke the mirror via SMSS on the principal. this only resolved itself after a restart of SQL on the mirror. not ideal. but from what i have encountered on google, not altogether uncommon either.
It's fine now, but mirroring is less robust than i had thought it to be.
roll on 2012.
🙂