i have a Toshiba Satelitte L850-13Q from December 2012, last month i send the laptop because the GPU maked problems, they changed my Motherboard.
Some weeks worked perfectly, but now i have some problems like before, i recorder sometimes when this it's happening and i upload on youtube, look here: http://www.youtube.com/watch?v=qiMC5QQzoSs&feature=youtu.be
I saw your short movie and must say GPU is acting crazy. Sorry but I think you must contact service again and ask for help. They must help you with this.
What you can try is to connect your notebook to external monitor, switch to external device only and make the same test, just to see if the same happen again. I presume the result will be the same and it is definitely GPU related issue.
If i don't have the latest drivers, do you think i would posted here?
The issue was caused by latest driver which was installed due to automatic Windows update.
The driver should be removed firstly and then you should choose another version available on the Toshiba page.