I told you it was untested! ;--)

Of course at some point you get to the last child, and $aheadtext->next_sibling; doesn't exist, so $more_text becomes undef.

So the test should not be while( $more_text->tag ne 'shead'), which will die when you trying to call the tag method on the undef value in $more_text, but while( $more_text && ($more_text->tag ne 'shead')).

Does that help?