See for instance http://develop.twiki.org/~develop/cgi-bin/view/Bugs/Item0?skin=print.pattern
. The table has an unstyled border. Looking in the source shows that no <div class="twikiForm"> is put around the form.
turns out that the printable tab was missing the ,pattern
and also that formtables.tmpl was out of date -
i removed formtables.pattern.tmpl, and updated formtables.tmpl with its contents