immutable bug?

[Peter Alexander]

On Saturday, 11 January 2014 at 21:16:55 UTC, Timon Gehr wrote:
> It is an implementation bug. Implicit conversion to immutable 
> is only supposed to work for strongly pure functions.

Can someone that knows all the details of the purity strength 
semantic differences please open a PR to get some documentation 
in the spec?

I've updated this bug with a comment: 
https://d.puremagic.com/issues/show_bug.cgi?id=7456