std.algorithm.copy and std.digest

When I use std.algorithm.copy on std.digest objects, I get different results compared when I am using put byte by byte. Why?

import std.stdio;
import std.digest.digest;
import std.digest.md;
import std.algorithm;

void main() {
    string s = "Hello!\n";
    auto d1 = makeDigest!MD5;
    auto d2 = makeDigest!MD5;
    foreach (ubyte b; s) {
        d1.put(b);
    }
    s.copy(d2);
    writeln(digest!MD5(s).toHexString);
    writeln(d1.finish().toHexString);
    writeln(d2.finish().toHexString);
}

Output:

E134CED312B3511D88943D57CCD70C83
E134CED312B3511D88943D57CCD70C83
D41D8CD98F00B204E9800998ECF8427E