Hi,
Looking at table 3-2 in the datasheet you can see that the default state of PortC (and the other Port regsiters) is unknown at power up, so one pin being high and another low is to be expected. If you need them to be in specific states when powering up you need to make sure to set them. However, you might considder setting PORT before TRIS - otherwise there might be a short pulse on the output between the output driver being turned on and actually being set.

/Henrik.