In Emacs I often get a box popping activated, but I don't know how it does activate nor how to deactivate it, because it is cryptic, I don't know what it is.
The box is conflicting with a very recurrent and ordinary Emacs command I use A LOT (it marks from the point to the end of the line), every time I press ctrl + shift + e, I get the box (in the point) overriding the Emacs command, making it unusable.
I run Emacs 25 over GNU/Linux Fedora 25 with GNOME 3 desktop environment. I checked the key combinations descriptions of GNOME, none of them has anything to do with the problem. Emacs is the only program I get the box once it gets "activated".
Restarting session nor the computer doesn't fix it. Reinstalling everything clean doesn't fix the problem either. To temporarily solve, I restart session to GNOME classic and the problem goes away, once the problem reappears in classic, then I start session back to standard, and so on.
Here is an image sample of the problem, see the dark grey box with the '@' character:
I am not sure this problem origins from updating the software, neither sure if it is just an Emacs problem, or in combination with another program (Fedora/GNOME). I have spent quite a lot of time searching, but I don't even know how to describe this thing to "google it" successfully, have not found any documentation from Emacs nor GNOME about this strange functionality.
What is and how to deactivate the dialogue?