This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
This has been around since public launch. The rotation widgets emissive material will cause trouble with the post processing and reflections in the scene. Especially troublesome if you with bloom and eye adaptation. It's a minor annoyance of a number of users. This was originally reported in TTP: 338322, but doesn't appear to have been brought over.
Work around: using the viewport Show flags and disabling bloom and eye adaption work for editing in the viewport purposes.
1. Open UE4 Content Examples
2. Use the ExampleProjectWelcome map that opens with the project.
3. Change to the rotation gizmo
Results: The rotation gizmo will appear in the reflections and under right circumstances can glow.
Expected: The rotation gizmo should appear like the move and scale gizmo.
Head over to the existingAnswerHub thread and let us know what's up.