Epics get removed from tasks when they are moved between stories

[Benjamin West]

We link our individual project tasks and stories to epics.    In WBS-Gantt, we indent stories under Epics and Tasks under stories, as shown below.  

We found that the epic is removed from the task if we move it between stories.   In the example, below, we would find that Epic 1 is removed from Task 1 after dragging Task 1 down as an indented task under Story 2.    How can we move tasks around without losing the epic link?

Project

   #Epic 1

         #Story 1

               #Task 1

         #Story 2     

Thanks in advance for your assistance!