[Zope] bobobase_modification_time problem

Hi, Due to a system clock error, our system's date was pushed forward a month; now the system date is back, ZopeTime() returns the right date, but any new object created still has the creation date a month into the future. Which is very bad, as most of the objects are time-dependent. Can this be changed, in other way than exporting everything and importing in a new Zope instance ? Zope-2.5.1, by the way. Thanks ! andrei