Small Bug Regarding The Power Options

(Refer to the attached image)
I had the "When I press the power button" setting set to "Shut down". I decided to change that setting to "Sleep". After I did that and pressed the "Save changes" button (did not ask to restart the computer). So after I did that, I pushed the power button on my Desktop Tower. Nothing happened. (This bug may only apply to certain motherboards, who knows.) So I said to myself, well let me restart the computer then try it. I restarted the computer, then once the computer loaded up, I pushed the power button on my Desktop Tower, and yay! The power button now makes the computer go to sleep now.

EDIT:
I tried pushing that button again after my post here, and that button doesn't work again! What happened?

Can someone help me out with this please? Thanks