I make no guarantees, but I can glance at the source code for updatedb. If I can locate the spot that prints "serialize," I can try to work backward and determine what conditions cause it to print that message.
I downloaded mlocate-0.25 (which includes updatedb), but a search for "serialize" within the code resulted in 0 hits.
What version comes bundled with FC16?
Alternatively, there would be nothing to prevent you from deleting all the mlocate database files and recreating the database from scratch. As far as I know, there is no dependence on "historical data" to create the database.
The man page for updatedb on my Debian system shows that the default location for the master database is:
Since that is the same location that you're reporting the other files, I think you would be safe to wipe out the contents of the entire directory and re-run updatedb as root (assuming that updatedb's "serialize" message is generated by trying to process/incorporate the temporary files in the /var/lib/mlocate directory).