Something is eating my roof!

Macro of a hole which is developing in the outer layer of fabric of the soft top of my car.
It now has a bicycle tube patch on it, and I'm waiting for some iron-on canvas from USA / EBay, but I'm concerned as to what is causing this, and what is going on under the patch.
Car is a BMW 118d, 2009 variety. Anyone got any knowledge of this?

(I refuse to pay the local BMW agency £106 + VAT / hour, just to tell me they don't know.)