When leaving an encounter page within a campaign, then coming back to the encounter I was working on items I had placed within the map layer are rearranging on their own. Example:
I had a grassy battlefield with trees, rocks, a horse drawn carriage, etc arranged on top of the grassy base. When I left the page and came back, many trees, rocks, and the carriage were shifted to the bottom of the priority list for the map layer.
Using Chrome with Windows 7.