Though what you are doing is not suggestible, yet if you need the flow as you asked, did you try to attach a
onkeydown
event on your submit button that will
override the onkeydown defined earlier? All you need is to override and
cancel the bubbling of event. Submit button will work as its normal behavior.
Try:
<input type="submit" onkeydown="javascript:event.cancelBubble=true;"/>