I have just upgraded my test site from version 4.1.6 (SVN) to version 4.2b.0 (SVN).
After the initial start of the newly upgraded 4.2b.0, I am taken to the Manage GEDCOMs page (as documented and expected). I am informed (as documented and expected) that the GEDCOM needs to be re-imported.
After the re-import, I no longer have ANY of the previous media information -- No media objects, and no media object links.
It appears as though the re-import assumes that the GEDCOM being re-imported contains the required media information.
This is NOT the case: My GEDCOM was previously re-uploaded and does NOT contain any media information because the off-line GEDCOM maintenance program (FTM) doesn't understand about media. That stuff is ALL in the database tables. During the re-upload, I'm allowed to tell PGV to preserve existing media tables, and that's the option I take.