Ah yes, this darnded thing. What it's doing is reading the button presses every time it runs through the events, which is very fast. You may want to have it set a counter to 0 when the button isn't pressed-- then have it set to 1 when it is pressed. Then do this:
Menu=0 + pressed down+ counter equals 1 >> change menu selection, set counter to 2.
That should work theoretically.
If you hold on a minute I'll try to do more exact events.
The easiest way IMHO is to use a flag. (You could just use a value for the same purpose but I find flags easier)
ABOVE all menu code have the event: Xmove up + Xmove down (+ any other dir you might need) --> Set flag 0 off.
Then in the menu code add the condition "flag 0 is off".
Ex: flag 0 is off + move down --> Do whatever to menu + set flag 0 on.
Then you can add whatever you want to that as long as you set flag 0 on.
It's important to have the "set flag 0 off" event above the rest or MMF will interpret it "wrong". (Actually MMf wont interpret it wrong, but your code would be contradictory to your purpose thus giving the wrong result)