what is the reason why there could be difference between dba_object.timestamp and dyana_version$.sti

When we pass a new version of a program to the production environment the dependent programs generates a ora-06508, we just need to recompile explicitly de dependent programs in order to overcome the error, why does this happens? However we have noticed that it doesn´t happen with all the stores procedures, just with some of them, is there a way we can known in advance that error ora-06508 is going to occur before it is reported by an end user.  The modified program as well the dependents program are in the same scheme, they don't call any remote program.