If it is not an issue of ABAP, then it would not be an issue.. :-)
Screen modifications you will not see in SQL trace.
Then I place my bets on a modification. Check what SPAU or SE95 has to say about SU01 or SUSR objects?
Cheers,
Julius
ps: are you sure there is no CUA involved? That would be the most logical and standard explanation for the behaviour.