If you use the 'allowdups' option and someone signs up for the second time to a list, the UID for that user gets set to '1' rather than retaining their previous UID as expected.
There is a typo in line 94 of signup.php where there are 2 commas in a row. Take out the double comma and it works again.
if(mysql_num_rows($result)>0){
list($xid,$xuid,$xcnf)=mysql_fetch_row($result); <-- this line
if($xcnf=='2' || $xcnf=='0'){