Noisy warnings now occur with this code (in dmd/druntime/Phobos master):


------------------------------------
struct Foo
{
	Object _p;
	alias _p this;
}

struct Bar
{
	import std.typecons: Proxy;
	Object foo;
	mixin Proxy!foo;
}

void main(){}
------------------------------------

Maybe, the origin is hashOf template function called by Proxy.