from the datasheet: "The alternate functions of P1.0, P1.1, P1.5, and Port 3 pins can be activated only if the corresponding bit latch in the P1 and P3 SFRs contains a 1 Otherwise, the port pin is stuck at 0.."

From the datasheeet:
"By (power-on) default these pins are configured as analog inputs, i.e., “1” written in the corresponding Port 1 register bit. To configure any of these pins as digital inputs, the user should write a “0” to these port bits to configure the corresponding pin as a high impedance digital input."

I have no idea, my guess is that this ambiguity in documentation arise from "To configure write a “0”" and ""to use, activated only if contains a 1". Another possibility is, of course, that the "write a 1" comes from when the AD techwriters did a cut-and-paste from someone elses documentation. If, indeed, the P1 register makes P1 a digital input when kept at a zero, it is very badly documented.

This seems to be a question for AD tech support.

Erik