Perhaps it's a Firefox problem? I'll try it in Safari (EDIT - seems to only trigger in Firefox, so might be a plugin conflict or something weird - probably wouldn't worry too much).

1) Load site, play

2) Get verb wrong - shows the hint table

3) Get to next question, first character entered into the box submits the form (usually incorrectly, of course!)

4) Normal behaviour resumes if I hit quit and play again