After pressing ? to enter a variable name, the autocomplete dropdown opens and stays open until (as far as I can tell) you either select an option or type a space, even if you've used a character that can't be part of the variable name (e.g. .; , )).

This means that if you type ?a ?b ?c. and press enter, you get ?a ?b ?c.SELECT even though ?a ?b ?c . or ?a ?b ?c. (note trailing space) followed by enter insert a new line as expected.

Screenshot showing how the dropdown is still open with the top result selected:

Demo: