Docs clearly state correct DSN flag to force new DB connections is "new". After hours of debugging, I found this in adodb.inc.php on line 119:
case 'forcenew': $forcenew = $data; break;
The flag the code is looking for is "forcenew"!
This could be easily be fixed by changing the line to:
case ('forcenew' || 'new'): $forcenew = $data; break;
Please... Fix this bug and save the next person all the hours of my life I wasted :-)