This is driving me crazy. Been working on it since last night and I can’t solve the problem.
Basically, in my 3D viewport my preview render shows exactly the material I want. In this examples, it’s a coloured pad with a wet map on it. However when I render, I get this really weird glossy glass-like material instead. It doesn’t make sense and it happens with any material I use (even a basic colour + diffuse shader). What the hell is going on?
Try turning off the material override in Render Layers - the pad material (and anything else) is overridden with the water material. But try to minimize the scene to the bare minimum that still has the problem.
Similarly, you can always activate renderlayers for what the viewport renders to check if something is up.