I've read this note about the short_open_tag option on
http://www.php.net/manual/en/configuration.php :
"Tells whether the short form (<? ?> ) of PHP's open tag should be allowed. If you want to use PHP in combination with XML, you have to disable this option. If disabled, you must use the long form of the open tag (<?php ?> ).
Maybe you'll want to take account of it for the next UBBT releases.