Revealed cards are still in the location they are revealed from until they are placed elsewhere. So when RBD tries to discard them, they are still being protected by FDC, which lasts until the end of the phase used, even if it is discarded by its ability.
So when both are active, you still place the revealed LS's in the LoB, and you still reveal the cards that would be drawn. But since the draw was "insteaded" to a reveal, they would return to the top of the draw pile instead of being drawn.
