I would be interested in hearing how you resolve all of thiese problems.
I had the same issues when I plugged a Seagate USB into an OpenBSd box.

Tar'inbg to the device appeared to work fine, revovery did not.

I just chaulked it up to my own lack of knowledge and moved on as I didn't
have the time to putz with it.

I played with 'mt' a bit and attempted to rewind, etc...nothing worked
for me.  I would have to assume you must rewind on your tape drive.

-mike