BY DESIGN:
This happens because the transform changes when the parent changes. It is not by much but it is different.

Before:
[0x0000000c] -3.82999945 float
[0x0000000d] 2.34999990 float
[0x0000000e] -1.15699959 float
After:
[0x0000000c] -3.82999992 float
[0x0000000d] 2.34999990 float
[0x0000000e] -1.15699983 float

A change in the Transform causes the geometry hash to change and we will do a rebake.

To reproduce:
1. Open project from 667255
2. Open scene baked
3. Select geometry > barrels
4. Move it out of geometry
5. Notice that rebake started

Couldn't repro it with simple scene, so not exactly sure what is causing this