On Thu, 18 Jul 2019, Harry Putnam wrote:
[ . . . ]
> Somewhere in the last few months my Debian OS has acquired an input
> box on upper right of base window (in X) that appears to grab any key
> presses aimed at the base window and print them in that small input
> window.
What you are describing sounds to me like a non-English-language character composer. Eg Japanese uses such to compose kanji characters from components typed one by one on the keyboard. Chinese uses one too, and so do many other languages, especially languages that need double-byte characters.
Have you, or could something have, installed any foreign languages recently?
Mark