Panning on one map in the mapeditor will pan another map if it's also open

[snipercup]

When panning a map in the mapeditor while also having another map open in the content editor, it will pan both maps.

Steps to reproduce the issue:

• Open two maps
• Pan to the right on one map
• Pan to the left on the other map
• Return to the first map and observe it's now on the left.