Icons getting "frozen" on screen?

This has just happened recently. As I was going to drag one of my ODT files into a folder for my experiment for school, it automatically got frozen and stuck to the screen. The ODT was in the folder, but an icon remained motionless, stuck to where I was dragging it. I left it alone since it didn't bother me much, but I couldn't drag things anymore or right click. I didn't know what to do, so I finally restarted it.

But I am still coming across this more frequently, and it is starting to bug me that I have to be really careful on how the way I drag things across the screen. And how i have to keep restarting the computer everytime this happens. What could it be?

The picture shows what I'm talking about. The red circle is where the ODT got "frozen" and stuck to the screen. I couldn't even click it or drag it or anything. It was layering every open application.