Assigning a Variant to another Variant which contains a large value type causes both Variants to have a reference to the same value. Currently this is not a huge issue because the only way to modify the Variant's reference to a large value type (that is, larger than Variant.size which is 32 bytes on x64), is through the use of peek on a struct. This will become a larger issue when std.variant supports static arrays however.

Sample:
import std.variant;

struct Foo {
    int foo;
    ubyte[32] padding;
}

void main() {
    Foo f;
    f.foo = 3;
    Variant v = f;
    Variant v2 = v;
    auto fp = v.peek!Foo;
    fp.foo = 6;
    assert(v2.get!Foo.foo == 3); // fails
}

Commenting out the padding makes this work as expected.