Vista - Bug in Vista if adding some Local Port

Hi,

I am not able to add a printer on a local port.
Actually if I am trying to create a local port and giving
the name as LPT4, an error message is popping up on the
screen saying 'LPT4 is not a valid port number'.

Actually I am having two PCI based parallel port cards
and Windows has assigned them LPT2, LPT3, LPT4 and LPT5.
LPT1 is assigned to Standard on-board Port.

But if I'm trying to add a printer on LPT4 port, I need to
make a local port with that name, but I am getting this error.

And one thing more, if I'm giving the port name as LPT10
and above, its working fine and creating the port successfully.

So, I would like to know is this the bug in Vista?? or Vista dont
allow user to create port with these names.

And the same thing I tried with Windows XP, its working fine
and I am able to create and add both ports (LPT4 and LPT5)
using Add Printer wizard.

So I want to know is there any solution to this or is it the
limitation in Windows Vista that user cannot create a local port
named as LPT4 or something like that.

Regards,
Anuj