I get this balloon box message.
You can move and interact but it prevents most of the keyboard releated commands, since every command goes to the text box. It can be removed but I don't know yet how, succeeded couple of times. And after it is hidden you can't reproduce with the initial way.
It comes to the left top corner, and when I go the menu (pressing ESC) I can move it and click help which opens MS IME Help, see attachment. {F20853} {F20854} {F20855} {F20856}
Ctrl+space and any other key
Finnish keyboard layout, English Steam.
I have never have or see this, i have no idea of what it is but i think its a background software in your computer and it don't come from Arma, just saying, need more information !
Try to look in the task manager, and try to see if it happen with other game/full screen software.
It comes only in Arma3. I checked from task manager while gaming and there was no new tasks/applications. I'm quite familiar with all the tasks in task manager.
Definitely not an Arma issue, you are probably changing your input language unintentionally by running and freelooking (alt+shift) and then invoking a input helper app from windows. Try looking at your language/input settings.