BUG: All connected wiimotes affect singleplayer.

[anon]

All connected input methods affecting the kart in single-player is normal behavior.

I understand that all inputs should be able to control the ui, for instance, but only the wiimote that starts a single player race should be able to drive that kart while the race is in progress.

Is the actual issue here that Wiimotes just laying around on a table still transmit input data that interfers with the input of the actively used one?

Yes.  If I connect multiple wiimotes, and then use one to start a single player race, the position of the other wiimotes interferes with driving.  Stk appears to average the data from all the remotes.  If the other three remotes sitting on the table happen to be in a position that stk interprets as turning right, I cannot turn left, and vice versa.