selected preview and speed differences

By the way, talking about fps…
Today I had time enough to work on my project,
in the Level Editor window, I lost around 50 fps.
I used to be around 100fps now it’s around 50fps.

Since we talked I didn’t touch a thing but those we talked about: Scalability settings, fps smooth and limitation, and Material Quallity.
Everything is set like before, as low as possible, no smooth, no fps limitation, I didn’t add anything in the code or in the scene. Actually even with an empty scene the fps seem to be locked up at 50fps.

Other windows seem to be working ok, this one bothers me though.
Any idea what I could have done on my clumsy way through those settings?