The documentation for the bpy.app.handlers.scene_update_{pre,post}
handlers states that they're called "on updating the scenes data".
However, they're called even when the data hasn't changed. Of course
such handlers are useful, but the documentation should reflect the
current behaviour.
Reviewers: mont29, sergey
Subscribers: Blendify
Maniphest Tasks: T46329
Differential Revision: https://developer.blender.org/D1535