--- Comment #4 from kloetzl <fabian-gcc at kloetzl dot info> ---
> And changing the algorithm to make no copies would not make it opaque, because
> the lack of copies would be observable. As the standard says, whether copies
> are made or not is unspecified. So if you want to treat them as opaque, don't
> do something that depends on the internal details, use them as suggested by
> note in the standard.
I see that changing the behaviour might be a bigger issue than the quirks
itself. Fixing this on the client side by changing the capture to by-reference
is trivial. I just fear that developers might waste quite some working hours
trying to figure it out for themselves.
Feel free to close this as wontfix/notabug. ☺