DrawDebug elements on screen affect aspect ratio letterboxing

During gameplay when the view target camera's aspect ratio is not exactly the viewport's aspect ratio, the presence of rendered debug draw elements (DrawDebugArrow, etc) makes the viewport's rendered area incorrect.

Specifically, the lower black area becomes larger when the camera aspect ratio > viewport aspect ratio. The right black area comes becomes larger when the camera aspect ratio < viewport aspect ratio.

User reported:

1. Create a new project with simple level.
2. Add a Camera Actor and set Constraint Aspect Ratio on the camera component to true. Also set the Aspect Ratio to 2 or similar, so we see the game through a letterbox.
3. In the level script On Begin Play, Set View Target to that Camera Actor.
4. Also in the level script, make a key press call "Draw Debug Arrow".
5. Notice the letterboxed area squashes up whilst drawing the debug info with the key press.