shifting array slices

[Ellery Newcomer]

I'm pretty sure this used to work:

import std.algorithm;
int[] ra;
copy(ra[5 .. 10], ra[4 .. 9]);

and would correctly shift the range [5 .. 10] down one
(unlike ra[4 .. 9] = ra[5 .. 10], which is prohibited by spec)

In dmd 2.057 of course it doesn't work; is this a bug or should I be 
looking elsewhere for this functionality?