Vista - Vista RC2 resets local printer ports on XP computers?

Vista RC2, apparently on its own volition, reset the local TCP/IP printer
ports used for many months on three XP computers connected to my network to
the local TCP/IP port definition it needed for printer connectivity. The
'new' Vista-generated port appears to be incompatible with XP, so printing
failed until I reset the local port to the originals on these three XP
computers.

So, does anyone have an idea why Vista RC2 does this; moreover, why does it
do this without announcing its intention? Since this behavior is, well,
'viral', how does Microsoft justify these changes to computers outside of
the Vista RC2 computer's operating environment?

Q