[igorius]

No, i dont have such apps... And no clue, i dont have windows.
I have tried restarting computer, didnt install any apps since time.
Even when calibre is the only app started, same thing.

Edit: Oh f**k, seems i had installed a new plugin: Column-helper. This one prevents the column-window showing in foreground!
Everything ok now.

Many thanks for your hints about disturbing apps. Only thing is, that it was a plugin!