1 ) open structure view of survey
2 ) select a different group
3 ) use "new question" in structure menu (not the big button in the main content area)
4 ) check group the question is added to
when you press add question, you can see in the breadcrumb that the group changes back to the previous selected group

if you press the add question button in the main area, the question is added to the correct group
and afterwards the button in the structure menu also works as supposed