Dozens of tapes showing up in library "slot 0" or no slot at all

For some reason, Netbackup lists dozens, maybe hundreds, of tapes as being in library slot 0, or being in the library but not in a slot. The tapes are definitely NOT in the library. They are all stored offsite, and verified to be at the offsite storage site.

We just noticed this, but it appears to have been going on for quite a while now.

The library is a Scalar i6000 if that makes a difference. Running Netbackup 7.0.1.