Hi Alan @cabriolet
I agree, it could have been there a while, and may historic, however all I can say is, it shouldn’t be there – the roof should be as smooth as if it was a Coupe’s roof.
I think you’re right in saying that it would be difficult, though not impossible, to peal back the roof’s covering. There’s the additional challenge that it’s likely glued down below the line of the front windscreen rubber, possibly necessitating removing the windscreen itself to give you the best chance as possible to peal back the covering with a view of gluing it back after instpection.
The alternative is to leave things alone, and just monitor the raised area to confirm it’s not getting bigger/unstable.
Gerben @gerbenharingsma , have you made any investigations of the bubbles you’ve found?