Disappearing icons (top RH corner)

Windows 7 64-bit. My "Minimize" "Maximize" and "Close" icons in the top right hand corner of my display sometimes disappear. This is a random occurrence and happens with my browser window. I like these icons to be constantly ON. I have tried to look for patterns, but can't put my finger on anything in particular.

1) Does anyone know why they disappear?
2) How do I prevent them from randomly disappearing?

Thank you in advance for your input and guidance.
 
Follow up: This is still an issue. Occurs randomly particularly when the computer is idle for a few hours. A re-start usually takes care of this and the icons are once again visible. This is not a problem; just an annoyance.

Can someone from the Windows Team look into this issue?

Thank you
 
You realize that we're just a bunch of regular Joe users here too, right? This isn't an official Microsoft Support site, so unless someone here has run into the same problem and happens to know the answer then I'm afraid we won't be able to help you...
 
Your point is well taken! Yes, I am fully aware of this fact! That is why I posted this here. I am also aware that this is not the official Microsoft Support site. This site has newbies as well as seasoned well informed computer gurus. Microsoft is a large company, but that does not mean that they have all the answers!

BTW, Microsoft monitors this site, and they have not responded yet! This speaks for itself.

This site has much more than the "regular Joe users", and I have a higher confidence level of finding the answer here.