Thank you for playing! :D
I've had a run-in with a similar issue regarding the button combos and came to a conclusion that it has something to do with hardware limitations, i.e. I couldn't press these combinations of keys outside of the game either. For me it was jump + every diagonal combination of arrows that's not up-right. Unfortunately, I don't know how to fix this or if it's even something that can be fixed. But thanks for the report anyway! I think my solution to this will be having fewer diagonal levels in the game, haha.