Attaching the bounding box gizmo to a mesh will automatically reset all mesh rotation values to 0.
Visual rotation is not reset for some reason, but the rotation values are.
PG: https://playground.babylonjs.com/#JI399Z
Open console, see rotation x value before attaching gizmo to mesh using pointer, and then check rotation value again after attaching.
tagging @Cedric
(this was an issue before the recent merge by the way, but I thought it was on my end then, hence the late report 
)
Not a bug. rotationQuaternion is used instead of Euler values when a gizmo is attached.
Why is this only the case for the bounding box gizmo? And is there anyway to force it to use euler angles instead of rotationQuaternions?
I guess it’s the case for legacy reasons that may have its roots before I joined the team.
This said, if you want to discard quaternion, ondragend observable, convert the quaternion to euler and set rotationquaternion to nul.