Nevermind. Found the problem using ISQL - apparently Firebird 2.1
changes TIMESTAMP precision from seconds to 0.0001 seconds, which is
causing difference between my OLD.MODIFIED_ON (4 decimal places
precision) and NEW.MODIFIED_ON (rounded down to seconds).

Can I force a timestamp precision in Firebird 2.1 to follow Firebird 1.5
rules?

Thanks, Pepak