Taking a second future from QPromise overwrites the first one

I'm not 100% if this is a bug as the documentation is a bit unclear, but in the following example I expected to get both callbacks instead of only the second one. If this is intended behavior, perhaps the second then() should print a warning that it is overwriting the old one.

	QPromise<int> p;

	QFuture<int> f1 = p.future();
	f1.then([](int i) { printf("first\n"); });

	QFuture<int> f2 = p.future();
	f2.then([](int i) { printf("second\n"); });

	p.start();
	p.addResult(5);
	p.finish();