original duration set to 0 when changing resource...

hi everyone !

a colleague of mine, working with P6 v6.2.1 had a strange problem :

he had, on every task of his project, an original duration and a resource (labor).

budgeted units calculated just fine, but when he went to replace the resource with another, the original duration suddenly went to 0.

I'm aware that UPT is subject to reset on its default depending on the option ticked (or not) in the user preferences tab, but I didn't find anything about the OD (at least for this problem).

every task in the project is set to "fixed duration and units/time".

for the record, I haven't been able to reproduce this strange behavior since he sent me the backup.

does anybody have an idea about what's going on ?

thanks in advance ;)