Noticed this while looking into a related issue.
The following steps re-order the UV layers.
Notice that before adding the torus the UV layers are UVMap, UVMap.001.
After adding the UVMap.001 becomes the first UV layer.
This looks to be caused by object join code.
| rB Blender | |||
| rB9f67367f0aae Fix T50084: Adding torus re-orders UV layers. | |||
When enabling Generate UVs the selected UVmap becomes first UV layer.
The change (UVMap.001 becomes the first UV layer.) happens not when adding torus but when enabling Generate UVs and only if the UVMap.001 is selected.
on Windows 8 Enterprise 32bits using with Intel HD graphics
Blender 2.78 (sub 4), branch: master, commit date: 2017-01-26 16:22, hash: 67bef6b, type: Release
build date: Fri 01/27/2017, 03:05 AM