I just found out that a rotator’s Pitch value is limited to -90 / +90 (that can be checked in the editor while rotating a mesh). Additional rotation is converted to -90/+90 by offsetting Yaw and Roll by 180°.
This is very painful when working directly with rotation components. I’m working on a simulation in which a plane has to control its attitude ; implementing a regulator with these values is very difficult. How can I convert the pitch, yaw, roll values back to a correct form ?
This behavior is very unlikely to be fixed ever, as any change would be likely to break all projects. The correct solution here is to use quaternions instead, which do not exhibit any such issue.