Using the shortcut "Ctrl + E" to open the static mesh editor in it's own floating window results in the camera locking in the upward position in the Main Viewport (*not* the viewport of the Static Mesh Editor).
Docking the Window to the editor resolves the issue.
1. In the UE 4.11 Preview 3:
2. Open a new Blank, First Person Blueprint project
3. In the World Outliner, select a static mesh cube
4. With cube selected, Ctrl + E to open Static Mesh Editor in it's own floating window
5. Back in the Main Viewport window, left or right mb
RESULT: Camera moves in a continuous upward path
EXPECTED: Camera to function normally, with full control
6. Now dock window to editor
7. Go back to Main Viewport window
RESULT: Camera functions as expected
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