Setting Actor's rotation in the editor is refused

I have an actor in the world. If I attempt to set the rotation in the editor to 0.0, 90.0, -90.0 then the editor automatically changes this to 90.0,90.0,0.0 instead.

Why is the editor overriding my required roll, pitch & yaw values and putting in it’s own? Even if I use 0.0, 90.0, 270.0 then I still get 90.0, 90.0, 0.0

When talking to members of Epic games they said that this was gimble locking. It’s because, whilst displayed as a set of rotations, underneath there is a quaternion. Setting this quaternion is gimble locking. The work around is to set slightly off of those angles of rotation to unlock.