Form: move element up sometimes without effect after save

In a survey with different containers, and the user want to move an element under a container (the container must contains some elements too). The element is not move above the container in the model but only in the UI. After saving and reload the form, the element is still under the container. There are different cases which root to the same problem:

• Survey editor and in e-Portfolio page editor has the same issues
• Move up an element above a container
• Move down an element around a container