Reproduction steps:
1. Open the attached project
2. Open the available scene
3. Select the '2' gameobject in the Hierarchy
4. Open the Animation Window
5. Create a new animation clip
6. Move the pointer in the Animation timeline to 60 frames
7. Slightly rotate the object along the x axis using the Rotation gizmo in scene view
8. Play the animation

Result: Rotating a gameobject (with the Rotation gizmo) that has children with offset position from the center of parent, will set the parent's rotation values to 180 when recording animation (see gif attached)

Reproduced with: 5.5.0a2, 5.4.0b25

Regression since 5.4