Never had a problem with the com port changing ever with or without XPort as a splitter (I have a better solution this year for a splitter)
I did also have problems using it with a splitter for running two programs at once (Dr Depth and OziExplorer with the depth plugin) and with a real serial port inputting NMEA depth sentences ... Once I ditched the Microsoft provided drivers and used the Prolific drivers out last May, I never had a problem again
Nothing more frustrating than trying to make a hydrographic map and all your depth readings are plotted in one place because the GPS decided to bail again ... Hopefully the GPS in the Gobi 1000 WWAN module in my new Acer One will play nice with my depthfinder/fishfinder, I'll have to use a USB to serial converter since there are no real serial ports available on the Acer netbook and oddly all three I have are all PL -2303 Prolific based even though each is a different brand
Netbook To Chartplotter Project