From Joseph Rézeau:
OK, your fix works when adding Branch tables (first description field has been made required).
However we have the same problem in the Question pages. The following fields should be made required:
Answer 1 / Answer (and maybe also Answer 2 / Answer as it does not make much sense to have a Multichoice question with only one choice to choose from).
Matching pair 1 / Answer (and maybe also Matching pair 2 / Answer as it does not make much sense to have a Matching question with only one pair to match).
Numerical question and Short Answer question
Answer 1 / Answer.
Correct response / Answer and Wrong response / Answer
and probably also the Page title and the Page contents fields should be made required in all question types...