This is still a bug in 7.5.4.2

A better and working query would be:
PHP Code
	 // How many users are in this group and another group
		$query = "
			select COUNT(USER_ID)
			from {$config['TABLE_PREFIX']}USER_GROUPS
			where GROUP_ID = ? 
			and USER_ID IN 
				(select distinct USER_ID 
				from {$config['TABLE_PREFIX']}USER_GROUPS
				where GROUP_ID <> ?)
		";
		$sth = $dbh->do_placeholder_query($query,array($k,$k),__LINE__,__FILE__);
		list($in_other) = $dbh->fetch_array($sth);
 

the other query will always return an empty set (0 rows) and always cause the group delete to fail..