Have you got a decode chart for the various keys and what they do? I see the 9/0 moves left and right while the next/prev keys go up and down. The 8 (zoom) function zooms in (and will circle) while the 3 key seems to go the other direction in zooming.
One thing I have noticed is that the zoom can stack keystrokes so when it finally finishes it can get past the zoom level you want. How can you enter the lat/lon you want?
It seems it works best if the unit was turned off before starting it, otherwise it may hang.