I was going to post about HALP! We can't play multiplaya!

However, I've since figured out a workaround for my initial problem, and now I have a bug report.

When playing splitscreen the mouse is constrained to the wrong part of the screen if it's used by any player other than player 1. For example if the mouse is used by player 2 while player 1 uses a gamepad, the mouse appears to be constrained to the middle half of the screen, rather than the right half. Different combinations of players create different mismatches, for instance if player 3 is using mouse while player 4 uses a gamepad (players 1 & 2 aren't playing), then the mouse can't reach the top quarter or so of the screen.

It appears that if the M+K player is player 1, the mouse always works correctly, although I haven't thoroughly tested all the combinations.

For now the workaround is to give player 1 M+K and gamepads to the other players.

I originally discovered this because player 2 had gamepad 2 assigned while player 1 used M+K, and since my gamepad is gamepad 1, it didn't work. Without checking this detail, I switched M+K to player 2 and gamepad to player 1, and frustration ensued.

There is also the MP HUD glitch. you can't open the pie menu when you use the keyboards controls if your HUD touched another unit's HUD.