When a form field before a group of radio buttons is removed from the document, and the page is subsequently reloaded, the check mark of the radio buttons moves upward.
Mozilla (and Explorer) remember the status of form fields if you reload a page, and restore this
state in the new page. However, when you check a radio in a group that's placed after a form field
that is removed from the form (removeChild()), Mozilla misremembers the checked radio
button.
Try it by checking "Test 3" and then reloading the page. You'll see the check mark moving to the left with each reload. If you'd remove two form fields, the check mark would move two radios.
This bug is likely related to Bugzilla's radio buttons move the checked on a reload bug.