Lightmass fails to use 3rd UV set

I have an emissive surface which displays a texture using the 3rd (index #2) UV set of the mesh. It looks fine in editor but when lightmass uses the material to calculate lighting it seems to use the first (index #0) UV instead what was specified.

Is there a fix or workaround? I need all 3 UVs (used with different materials) for lighting throughout the scene.