When a sprite, rendered on an object, that is rotating around Z axis, is flipped (either on X or Y axis), the sprite starts rotating around Y axis, becoming thinner.

Steps to reproduce:
1) Open the attached project.
2) Enter play mode.

The scene contains an object that has a child with Circle Collider, which is attached to the parent with Fixed Joint 2D. When the circle starts rolling, the whole object starts slowly rotating around the Z axis, but the sprite is rotating around the Y axis as well, although the Transform of the object doesn't indicate that. This happens when the object is flipped on X or Y axis.

Important note: This issue doesn't show up when in Scene view.

Reproduced on:
5.6.0b5, 5.6.0a1

Did not reproduce:
5.5.1p1

Tested on:
macOS 10.12.2, Windows 10