Zandronum

The ACS function SetSkyScrollSpeed works fine in single-player, with or without multiplayer emulation, but doesn't seem to work in client-server mode.
I have attached a minimal test map (MAP01): In single-player, using the switch changes the sky, and the sky starts scrolling. In client-server mode, the sky changes, but does not scroll.

Am I doing something wrong, or is this a bug or feature request for the tracker?

Is something supposed to happen, but isn't? Then it's a bug that goes on the tracker. And if you're wrong, then eh, you'll probably still get to the cause of it.

Appears to be a bug in the engine.
At first I was thinking that maybe only the server could make those sort of changes, but even then it still doesn't work. Head to the tracker and report it.