[gnome-db] libgda doesn't open transactions

branch 4.2 (last commit), postgresql 8.4, windows

i have a strange behavior of libgda: on 2pc (a winxp and a win7) it  
doesn't open transactions and it doesn't return errors

tested with gda-browser: when i click on begin button nothing happens  
(commit and rollback buttons remain disabled)

version 4.2.10 works; and it works also on my pc where i develop and  
where i have 4.2.12 HEAD; environments probably are not the sames, but  
libgda and libpq are at the same version

what could be the problem?

thanks in advance