[Zope] bobobase_modification_time stuck after system date change (back 1 month)

Hi, I installed a brand new Zope on a server (redhat) on which the system date was 1 month ahead (2003 March 3 for today). The system admin just corrected the system date/time today, but when creating a new object after this, its bobobase_modification_time() is still shifted 1 month ahead, when DateTime() shows the (corrected) system date !!! Even after a Zope restart. Why does this happend ? How can I fix this ? Many thanks in advance for any hint ! --Gilles