Groupbox preserves empty indentation spaces (encoded as  ) in the rendered client HTML. If tabs are used, they are stripped. See the example below. Label 1 and Label 2 use tabs (and are displayed correctly). The rest of the labels are idented using spaces, dislocating them.

See: http://zkfiddle.org/sample/17h1sue/1-Groupbox-bug-nbsp-added-at-Client-because-of-indentation