intercepting keyboard shortcuts in an app

i am running Xubuntu 18.04.5 with a keyboard shortcut set to have the PrtSc key run a program that captures a screenshot. i ran across an app that is reacting to that. i have a text input open in an app named "Gramps" (genealogy software) to type in the name of a new family tree. then i press PrtSc. it closes the input and sets up the default name.

i thought a shortcut key press would not be received by anything else. how can it be doing this? the app runs in Python3.