From T214197: Pressing backspace next to a selected item/pill converts that namespace back to its namespace number. Given that the widget doesn't expose namespace numbers to the user anywhere else, we should probably try and stick with names.
This should be fixed by overriding doInputBackspace from TagMultiselectWidget in MenuTagMultiselectWidget. The menu options display the label rather than the data, so it makes more sense to populate the input with the label.
- Pressing backspace next to an accepted item/pill should replace the pill with the namespace name, not the number.