I had a problem similar to this, and this is how I remember fixing it. I'm not sure if the commands are exact.
To my knowledge, or at least on my computer, the date command only adjusts the date or time for that session. I had to syncronize it with the hardware clock to get it to change permanently. "hwclock --systohc" I believe was the command I used (after running date to change the system clock).
Also, you can change the hardware clock (hwclock) directly by the "hwclock --set --date="05/18/2007 18:00:00" and then "hwclock --hctosys", which should syncronize it with the system clock.