I have an 1.1.1 unlocked, jailbreaked iPhone with Windows Vista Home Premium and iTunes 7.4.

Date & Time settings on iPhone are:

i. Set Automatically - On
ii. Time Zone Support - On

I have iTunes open and then I connect the iPhone cable. The date and time will change randomly to 1 month earlier and the time, a few hours in front or behind.

Example: Today is Dec 1, 2007. 12:45am.

When iTunes is already open, I connect iPhone cable. Date/Time changes to Nov 11, 2007 at 7.44am.

How to workaround?

Never open iTunes first. Connect iPhone cable first and then, open iTunes.

Why does this happen? I have no idea.

See here and here