Unable to unlink materials on duplicated object

Hello,

I'm having trouble with a model in Stager which has a material and an image applied to it. I want to be able to duuplicate the model and change the image on the duplicate.

I understand that by default Stager links materials, so I've been through all the instances of the materials on both models and clicked the unlink button in the properties panels. The link button then disappears for all instances.

Unfortunately the materials images still seem to be linked and changing one still alters the other. Restarting stager gives the same result.

Has anyone experienced this?

Many Thanks

Ed