lost cmos from powerdown

I have a gateway 2000 p5-133. I setup the cmos and can boot up ok just as long as I don’t use windows to restart or shutdown the computer. I can hit the on off switch while in windows, and I keep my cmos settings. The strange thing is once I lose the cmos settings, I have to clear the cmos with the strap on the motherboard to have the hard drive auto detect again.