I can confirm that Charles' solution works for me too so that gives you a solution that better aligns with your original request and doesn't require any form redesign. However it has a secondary effect that you may want to consider. It doesn't allow the user to use Tab or Shift-Tab to move between form fields.

So I guess you need to decide if the majority of your users move around the form with Tab or with the Mouse.

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Andrew Lockton
Chrysalis Design, Melbourne Australia