When in the edit questionnaire screen, there is a "Questions" section. When button "Add an existing question to this questionaire" is hit an "Add Question" popup box appears. in this box you "Type part of the question you want" and then you can only cancel. There is no submit/save/select.
Did I miss something?
Edit Questionnaire
Re: Edit Questionnaire
Looks like the recent update in the jQuery library has broken the autocomplete. The library has now been incorporated, with different semantics, in jQuery UI. I've just pushed a fix for this to Github, let me know if you still have problems with it after this.