Interesting. If you use CTRL-Scroll Lock, it does register correctly.

Another interesting thing, if you do not assign the scroll lock key, pressing it will toggle your indicator light on the key. If you do assign it, it will be triggered twice, like OpenMPT also triggers scroll lock and thus undoing the action aka triggering itself.

In fact, if you set scroll lock as a key-up action, holding down scroll lock performs the action, then releasing scroll lock will undo it.

So OpenMPT does actually trigger the action, but it does it twice which undoes the previous action.

Yeah, it seems like the code that prevents the caps/num/scroll lock keys from lighting up creates this problem (the other two keys have the same problem). I'll see if I can come up with something clever that prevents them from lighting up but still work as expected.

Right.

What I'd do is when a keypress is given, Set a variable that we've received the key once. (like a counter) When the action is triggered again, the counter is raised another time. If the counter hits 2, its reset and the actual action is performed.

Yeah, except that exactly this is being done and it doesn't help because OpenMPT's input system is a bit more complicated than that. You really don't need to help me with programming.

Fixed in r3723.