Hmm, this could be a macro with event “Character Inserted” or like that.
Check menu “Macros > Customize…” if there is a macro listed which have a event assigned.
Or perhaps you run a “automation” tool like AutohotKey or like that.
Check from Task Manager (Crl+Shift+Esc)
Are you the only one who work on this PC? ;D
I get no better ideas right now…