Edit Layers corrupting landscape material

Firstly please excuse the duplicate post. I think I posted wrongly in Rendering and do not seem able to move it. So if a mod wants to delete the other, that is cool.

So I have applied a material to a landscape and it looks as it should but on enabling edit layers, boom, completely messed up - can anyone comment on cause/solution. Thanks.

after enabling edit layers:

Surely someone must have some ideas on this.