X axis rotation only follows relative rotation

A user is reporting that the X axis rotation appears to only rotate based on the object's relative rotation, and not rotate based on the world rotation, even when using Set world rotation.
For testing this issue I created an Actor class BP with a static mesh component and tested the differences in the relative and world rotations. The Z and Y axis behaved as expected, changing directions appropriately when switching between Relative and World rotation; however, the X axis never changed, it consistently rotated the same direction, regardless of Relative or World rotation.

Regression:
This issue occurs in 4.15.1, 4.14.3, and 4.13.2 binary versions

1. Open Test project Provided
2. PIE
3. Press X (result)
4. Press Z (Expected Result)
   Result: X axis rotation is always following Relative rotation
   Expected Result: X axis should follow world rotation