This is not a memory leak.  The reason perl allocates memory during 
printing is that it converts all the 0 values in the hashes to strings 
and stores these.  This upgrades your SvIV structs containing 0 into 
the much larger SvPV structs containing both 0 and "0" (see [1]). 

--Gisle 

[1] http://search.cpan.org/src/GAAS/illguts-0.09/index.html#sviv