The game has gravity so p2 sinking is normal. P1 going up tho means it was thrusting on its own, which is bad. is it a 360 controller? If not it's probably my fault by having joysticks enabled by default without a config. Thrust is mapped to the 360 controller's right trigger currently.
They're PS2 controllers but... one sec.
Okay, I've checked and they're working by default. I'll reboot again soon but I'm pretty certain something must've been held down or wonky on startup.
I assume it's currently normal for the controllers
and keyboard to work simultaneously? Depending on how they interact that might be an interesting 4-player meta-game with enough beer

EDIT: After further experimentation, P1 is bound to the joystick which must be partially incompatible because that ship has thrust stuck on no matter what I do to it (short of unplug it, I assume). All the other commands work fine, as far as I can tell... they're bound to something or other on the joystick and also work on the keyboard.
P2 is bound to one of the PS2 controllers which is
almost compatible. Everything works except thrust which isn't bound to anything but is still overridden on the keyboard (as it is by the joystick for P1).
I've got family visiting in... about 10mins, so I'll have to unplug all the game controllers later to get a feel for it.