GP’s point is that many keyboards these days come with a Mac/Windows switch, and one of the things that switch does is swap the keycodes sent by the Alt and Win keys—the “Mac” behaviour is exactly what you’re describing. (The other thing it does is toggle FnLock for the F-keys.) So if I had a problem like yours with my keyboard I’d think that the Mac/Win switch were in the wrong position. If I’m reading page 9 of the manual[1] right, on the K4 the switch in question is right next to the USB-C port.