I've had my fair dose of fun when using 1wire. As to why things should change from P3 to P1, I'm not sure. Did you change all references to P3 over to P1? What killed me with 1wire was cable length and the port characteristics - the pull down ability of the port pin was not sufficient in my app and that caused a lot of unreliability. Using the Dallas suggested driver using a 2n7000 mosfet to pull down the bus made things a lot better but I ended up using their expensive i2c to 1 wire ics as I had space issues. I was only using 3 metres of wire - you need to use twisted pair otherwise you will have problems. CAT5 cable does well. I had many hours playing with the timing to no avail - 1 wire is reasonably tolerant of timing, so if you're sure your timing is within spec, start looking elsewhere. I was using a DS2430 eeprom device that are parasitic powered, look very carefully at the 0V voltage on the port pin with an oscilloscope - mine was not going low enough and you can have undershoot problems as well. The Dallas 1wire driver ics also have active pullups that make the signal look much cleaner. Hopefully these suggestion might shed light onto your problem.