Key violation

Hi there!
I've got an interesting question: I use Paradox+BDE, and when I try to
INSERT (SQL) a record that's already in the table I receive "Key violation'
(of course); BUT - it only happens with INSERT VALUES (...), but not with
INSERT SELECT!! in other words, when I try to insert a number of records at
once, it all goes 'silent'. So what happens, does anybody know?