Attempt to free unreferenced scalar wanings with threads

Hello,

I'm trying to make one of my programs multi-threaded using perl 5.8.1 
and threads.pm. It seems to work just fine except that when each thread 
exits (I think) it emits a warning like:

Attempt to free unreferenced scalar at 
/usr/local/lib/perl5/site_perl/5.8.1/i686-linux-thread-multi/DBI.pm line 628

Each thread has it's own database handle, so each one prints out several 
warnings. By the time the program is done, it's printed hundreds of of them.

I can't for the life of me figure out what it means or how to fix it. 
I've search the web and newsgroups with no avail. So at this point, I'm 
just looking for a way to disable this particular warning. Anyone know 
if it's possible?

Thanks in advance,
Javier