If you create a checkbox field with more than 9 choices, the form skips 10 when it renders.
<li class='gchoice_1_9'><input name='input_1.9' type='checkbox' value='9' id='choice_1_9' tabindex='9' /><label for='choice_1_9'>9</label></li>
<li class='gchoice_1_11'><input name='input_1.11' type='checkbox' value='10' id='choice_1_11' tabindex='10' />
This causes the problem that the last checkbox is not saved when checked.