Display went haywire

So, I was working in my Ubuntu 14.04 desktop. I had Mozilla, LeafPad and Libre Office CALC was open. I did a alt-tab to get back to CALC and click on an empty cell. Then it became this. It happened multiple times. The CALC spreadsheet had only small amount of data.

Any idea?

Was Calc the only affected ?

Looksto me like a problem with your video card.

@rautamiekka - I did not try in Write or presentation.

@horst - I have nVidia card and driver is installed properly. I will check if I can get something from log.

I mean whether the other programs were affected too. Since the screenshot shows the entire desktop affected, it has nothing to do with Calc.

Here’s what I did:
I figured that Unity is too heavy for my desktop configuration. Thus I installed Gnome Metacity, then it never happened again,