I hijacked the level end routine to warp to credits after the end of the level. This works great when I take the secret exit, or the "boss exit" (ending the level by killing a boss), but not the main exit. When I do take the main exit, the first part of the credits (the staff roll) is completely black. The music still plays, however, and the further parts of the credits work fine.
(Base2 is $6000 when using SA-1, $0 otherwise)
This happens both with SA-1 and without.