In pause key events are sent to the MSX, which means that while replaying with the reverse feature it will switch to record mode.
replay mode, pause
press and _release_ keys
This happens for instance when you accidentally type a key in the openMSX window while it's being paused.
I was thinking that the correct behaviour would be to stop sending keys to the MSX in pause, but when unpausing, resync the key status with the MSX (in case you want to press a key and already did that in pause and then unpause to have it effective immediately).