When you remove an element by innerHTML='' it's possible to re-append the element to the document. In Explorer Windows, though, the text goes missing.

Explorer Mac loses track of the element when it's been removed. So in this browser elements don't stay in hyperspace after they've been emptied from the innerHTML.

Test page. Workaround is not included.
Reported by ppk.

Explorer Windows and Mac, Mozilla and Opera see <fieldset>s as form fields, even though the spec doesn't mention them in the list of control types.

Mozilla and Opera allow change events on <fieldset>s, even though they don't make sense.

Test page. Workaround is not included.
Reported by ppk.

Mozilla sends extraneous events with improper and invalid event.relatedTarget values instead of generating simple pairs of mouseover/mouseout events.

Test page Workaround is included
Reported by: Garret Wilson.

When a drop-down menu has a long option, and the form is placed inside a div of a shorter width, the option is cut off when the user scrolls far enough to the right.

Test page Workaround is not included
Reported by: Chris Hester.

Once the background-color is set on an element, subsequent 'background:inherit' rules (even those matching selectors of higher weight) can't cause the element to inherit the color from its parent.

Test page Workaround is not included
Reported by: Pierre Saslawsky.

When nesting a form wholy inside a cell certain browsers includes extra white space at the end of the form. This would appear to be a bug.

Test page Workaround is not included
Reported by: Jay Soffian.

If options in a form are given a large enough height and there are too many options to fit the screen, Firefox will display the menu upwards, leading to it being cut off.

(ppknote: Mozilla is the only browser that honours a height on options. Nonetheless this is certainly a bug.)

Test page Workaround is included
Reported by: Chris Hester.

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.

Test page. Workaround is not included.
Reported by ppk.