Play a map with Nightcore mod
Watch the replay
Turn off Nightcore
The speed/pitch is correct, but you still hear the added sounds (claps/cymbals/beats etc.)
Also, if you watch a replay with NC, and set play back speed to 0.5, it'll be normal pitched, but if you disable NC, it'll be lower pitched
Even more: If you set play back speed to 2, with NC on it'll be incredibly high pitched (<3), with NC off it'll be pitched like NC normally
So many NC bugs O.o
Kinda off-topic, when was x2 replay speed supported for DT/NC?