Temporary Image Retention (aka. "ghosting") on XPS 12

I am working with my new XPS 12 (Core i7, 256SSD, 8GB RAM) since January '13. In the last few days I recognized a Kind of "ghost" pictures. When I work for e.g. 5 to 10 minutes on the Desktop and then switch to the Start menu, the Windows task bar shines still through very slightly. It can also be reproduced very good with the following steps:

1. Look at a bright web site (like this) for about 5min
2. Switch to Paint and fill the area with a dar grey (e.g. HEX:404040)
3. Zoom the Image to fill the whole Screen

Now you can see the web site from before shining through!

Is this a normal behavior? Are there any other XPS 12 users who can reproduce the problem? Or may it even be a hardware defect?

Cheers,

DeHoba