
I bet it suddenly started sticking when you  started leaving the PC running the
menu all night.  There is a limitation/bug in the date roll-over software in
PC's that means you have to be doing something like waiting for keyboard input
via a DOS call rather than a BIOS call (as menus often use) otherwise the code
to update the date after midnight never gets called. 

Somebody might be able to correct the details in case I've mis-rememberred
them, but I think you have to change the menu program (if you have the sources)
or add a TSR or system patch or something.  As far as I know the CMOS clock
keeps the right time (in fact about 7 seconds/day better than DOS's clock).