Hello 
I am new to zBrush and still exploring the awesome Tool 
Here is an issue I came across:
I have a tool with 6 subdivision levels and different layers. I click on “UV Master” and “Work on clone”. Then “Unwrap” and after this I want to see it “Flatten”. Clicking on the “Flatten” button gives me a message: “Flatten is only allowed on mesh without subdivision levels (use WorkOnClone/Copy/Paste UVs system).”
So I make sure that I’m really working on the clone, go to its geometry and see that it says I’m on subdivision level 1. I delete all higher levels (after I activated the layers and made sure that I have no recording layer) and then I can flatten the UV. What I dont know is why I have to do this manually since it wasnt mentioned in the UV Master Tutorial Video =D
Is there a better solution or did I do something wrong even if I followed step by step shown in the Video?
Have a great time everyone =D