Assume you have a model that uses a set of UV Maps for different sections. For example, the character in the image aside consists of a Head, an Upper Body and a Lower Body. Each of the parts has got its own UV Map and each map i.e..: Head UV, Upper UV, Lower UV:
The UV Face Copy Tool
You can either merge other UV Maps to the current active UV Map, or you can distribute the active UV Map to other UV Maps
To: Copy all other UV Maps to Active UV Map
Below the direction chooser you find the list of available UV Maps in your model. here you can select which maps shall take part in the Copy action.
This option restricts the copy to the selected UV Faces (actually UV Vertices) .
The button at the bottom of the panel executes the Copy tool.
Note: The UV Face Copy Tool only appears when the Model has 2 or more UV Maps.
In this example
- Add a new UVMap as Target Map.
- Select the new Map as Active Map.
- In the Copy UF Face tool Choose From.
- Select all other UV Maps
- Then Copy to UVMap
However this is not a bug, but it is a consequence of how UV mapping works after all.