I tried what you said. With the delay_before_history_dat' set to 1, it displays and scrolls all the way through the game info and then starts back at the top again - as expected (and only for the selected game). When I set it back to 0 it's the same issue again where it goes back to the snapshot and then the movie. I tried changing both the movie and snap to paths that don't exist to see if maybe the interference was there - same result.
To make sure that only the up and down are being used, I used the arrow keys on my keyboard - no difference.
Am I correct in assuming that the history reader is built in to Mamewah? If so, it seems like it almost has to be some sort of issue with the format of the file or a config setting somewhere. Otherwise, why would it work fine for MAME?