OK, I think i see the problem now, the simple page did help, thoug you have one problem on that page.
The child list is named "contactID" on the simple page and "contact" on the other one.
I believe this for the body tag should do the trick:
<body onload="<? if (isset($_GET['ID'])) { ?> WA_setSelectionsInChildList(MM_findObj('orgID'),<?php echo $row_project['agency']; ?>);<? } ?><? if (isset($row_project['agency'])) { ?>WA_FilterAndPopulateSubList(contacts_WAJA,MM_findObj('orgID'),MM_findObj('contact'),1,0,false,': ');WA_setSelectionsInChildList(MM_findObj('contact'),<?php echo $row_project['contact']; ?>) <? } ?>">