This display behavior just started happening in Moodle 2.6:
I need to edit some courses so I go to a course, and click the "Turn Editing On" button. I go to the activity I want to edit and click the Edit button. Click the Edit button collapses the Activity bar and throws the Edit button to the left. If I go to the new location of the Edit button and click it again, it returns to the original position, and displays the Edit menu.
Also the page is allowing me to reorder the activities, which it had never let me do in the past. However, the drop part of the drag-and-drop makes the activity bar disappear. If I click another activity bar, the previous activity bar reappears.
I think there is expand/collapse code that is triggering whenever I click on an element in the activity bar. Is there a way to turn off this functionality or at least ignore it when I click a control within the activity bar?