ReactOS MUST work on non-ACPI systems.
 On ACPI systems, ACPI will enumerate all your serial ports, even
 non-standard ones.
 On all systems (ACPI and non-ACPI), standard serial ports will be
 probed to test their existence. 
 I think, to correctly enumerate com ports  in this situation, you need
 to remove enumeration
 code from pnp routines. What do you think about creating something
 like SerialEnumerateComPorts() routine
 and call it from DriverEntry? If you are not working on this now, I
 can try to implement it. The enumeration process
 is described in "Enumerating Legacy COM Ports" article from DDK.
 
 Oops, I  haven't seen  your latest changes from svn.
Maybe you already did it...