In Impulse Tracker, S91 turns on "pseudo-surround" for a channel, but S90 doesn't do anything. Currently in Schism S90 resets panning to center, regardless of previous panning or default panning for that channel. (modplug behaviour)

I think it would be great (and very useful, to me at least) if S90 would reset the channel's panning to its pre-S91 state. This way, when putting some echo notes in surround, you wouldn't have to repeat the channel's normal panning each time - which makes it kind of cumbersome to change the panning of a whole passage that has many S91/S8x commands.

I don't think this would break compatibility with anything, or playback of older .IT modules as far as i can see (how many of them have random S90's lying around?)