When trying to reorder groups directly on the "Structure" tab, they shift unpredictably, and in the process, certain questions are lost from their groups (they still show up under Settings-->List questions, but without an associated group).

This is a VERY serious issue that has just resulted in the loss of an entire semester's worth of research data for me. This happened because I hadn't noticed that a number of questions were missing before administering the survey to the group. I am very sad...

Note: reordering via the "Reorder questions/question groups" tool does work correctly.