They won't clean themselves up sadly. In my incident, it happen mid session so knew it wasn't to do with cool down lap or holding foot brake on in paddock. The OE spec pads after a few laps of Silverstone National, overheated and begun to deposit on the discs.
A brake bedding in process is very much worth a go, as this sorted mine out. Sounds strange as excess heat essentially caused the issue and now you're using heat again to remedy.