How old were these "old" monitors and have you guys tried to connect them to other "disposable" VGA cards for testing? The only thing I can think of is maybe these monitors are old enough to not be DDC compatible and for some reason have the key pin (#9) grounded. DDC uses that pin to supply +5V so the EDID can be read even with the monitor off. This could possibly explain why the part smoked even with the monitor off, though it's only supposed to supply 50mA. It might also explain why the VGA port still works, since DDC is not necessary for the operation of a monitor. Still, if the monitor wasn't DDC compatible, there shouldn't have been a pin there, unless it wasn't the original cable.
A simple test to see if DDC is still working would be to plug in a modern VGA monitor, without the power cable connected, and see if the PC can still identify it. Or, if you have a multimeter and steady hands, test pin #9 for +5V.