Calling dynamically bound functions from weakly pure function

[Timon Gehr via Digitalmars-d-learn]

On 07/19/2014 03:53 PM, Kagamin wrote:
> It's ok to deduce opDispatch as pure, but then its purity should be
> enforced and error reported.

Why would it be ok to deduce opDispatch as pure only to report an error 
that it is not actually pure? This would be a bug as well (albeit none 
that causes unsoundness.)