Difference between dstring and string format specifiers support. Bug?

[Vadim Lopatin via Digitalmars-d-learn]

On Wednesday, 9 November 2016 at 08:21:53 UTC, Vadim Lopatin 
wrote:
> Looks like bug.
> dchar[] and wchar[] format strings support less specifiers than 
> char[]
>
>         import std.format;
>         string test1 = "%02d".format(1); // works
>         assert(test1 == "01");
>         dstring test2 = "%d"d.format(1); // works
>         assert(test2 == "1"d);
>         wstring test3 = "%02d"w.format(1); // fails
>         assert(test3 == "01"w);
>         dstring test4 = "%02d"d.format(1); // fails
>         assert(test4 == "01"d);

dmd 2.072.0