Can some one help ? Screen grab has turn vampirish. The highlighted portion does not disappear after grab

As I wrote, the highlighted screen grab window stays on, even after the screen grab quits. This is very disturbing because one has to reboot to get rid of the highlight. If one tries to screen grab a portion of the screen and highlights it, screen grab creates the file, but leaves the highlighted area on the screen, even after screen grab quits.

I had this problem with other macs, my macbook pro was immune until now. This is a serious bug, for one either forgets about using screen grab, or uses it and reboots. Also, why isn't the screen grab shown in the window with the Force Quit Applications ? It is a system app, isn't it ? One should be able to force it to quit.