union alignment

[tsbockman via Digitalmars-d-learn]

Is this a bug?
---
module app;

union Foo(A, B) {
    A a;
    B b;
}
void main() {
    alias F = Foo!(double, ulong);

    import std.stdio, std.algorithm;
    writefln("sizeof:  (%s >= %s) == %s",
        F.sizeof, max(double.sizeof, ulong.sizeof),
        F.sizeof >= max(double.sizeof, ulong.sizeof));
    writefln("alignof: (%s >= %s) == %s",
        F.alignof, max(double.alignof, ulong.alignof),
        F.alignof >= max(double.alignof, ulong.alignof));
}
---
Shouldn't a union type always have an `alignof` at least as great 
as the `alignof` for its largest member?

DMD 64:
sizeof:  (8 >= 8) == true
alignof: (8 >= 8) == true

DMD 32:
sizeof:  (8 >= 8) == true
alignof: (4 >= 4) == true

GDC 64:
sizeof:  (8 >= 8) == true
alignof: (8 >= 8) == true

GDC 32:
sizeof:  (8 >= 8) == true
alignof: (4 >= 8) == false  <<===== Bug?

LDC 64:
sizeof:  (8 >= 8) == true
alignof: (8 >= 8) == true

LDC 32:
sizeof:  (8 >= 8) == true
alignof: (4 >= 4) == true