D 2.066 new behavior

[Paul D Anderson via Digitalmars-d-announce]

In all previous versions through 2.066 beta 5, the following code 
compiled and ran correctly:

import std.stdio;
T add(T)(in T x, in T y)
{
        T z;
        z = x + y;
        return z;
}

void main()
{
        const double a = 1.0;
        const double b = 2.0;
        double c;
        c = add(a,b);
        writefln("c = %s", c);        // 3.0
        c = 1.0;
        writefln("c = %s", c);        // 1.0
}

From beta 6 onward it no longer compiles. The problem seems to be 
const qualifiers being carried into the template type. Since a 
and b are const double, the function template parameter T is 
const double. So x and y are const, no problem, but z is now 
const also. The following error message is given.

T add(T)(in T x, in T y)
{
        T z;
        z = x + y;              // Error: Can't modify const expression z
        return z;
}

The same problem shows up elsewhere as 'cannot implicitly convert 
const x to x'
and 'none of the overloads are callable using argument types (x) 
const'.

Is this expected behavior that has never been enforced before, or 
is it something new?

And is anyone else having the same problem?

Paul