Well, that is not the way how the full screen mode displays to me. I have also tried Chrome and Safari. So, it´s a problem with my wordpress configuration. Some time ago i disabled all the plugins, but the problem persists.

Have you tried the “just writing” plug in, and the problem i also described, that for sure, is related with the previous one.

Thanks for the answer, but in the meantime discovered the problem. The names of the image files were too long and had spaces. Changing them solved the problem.