I was spectating this person with no issues. Then I downloaded a map and...I don't know, maybe it was just really coincidental timing that caused the bug, but when he started playing the map, this happened. It's still spectating, but animations from the main menu are playing at the same time (kinda fun watching the little osu! logos snow down against the black background....can we have an option to always have those? >.>). The buttons in the top right corner work, but cause issues with the spectating. For example, going to next or previous track resets the play to the start and causes the playback speed option to not actually change playback speed. The map itself will only appear if you go back to the correct song (along with cursor movement), but the hitsounds will play regardless. Pressing stop causes the play to constantly freeze and jump. The bug persists if I stop spectating and start again.
I don't actually know if this bug is specific to cutting-edge (and don't know how I would try to replicate it to find out), but I'm using cutting-edge, so I'm posting it here.