When I've had this happen nothing in the game could be interacted with at all. No tooltips for hovering over units, no clicking of any UI elements, it was just totally frozen. Yet just like the OP the music kept playing and the mouse was still movable and still looked like a feather. Had to minimize the game and end the process after a few minutes of nothing happening.
Something similar happens very often when I try to load a game. It just get's stuck at the "creating world" screen playing music but doing nothing else. Not sure if it's related.
