[atomics.types.operations] Possibly unintended example

The example in [atomics.types.operations] Note 8 currently reads:

union pony {
  double celestia = 0.;
  short luna;       // padded
};
atomic<pony> princesses = {};

bool party(pony desired) {
  pony expected;
  return princesses.compare_exchange_strong(expected, desired);
}

In common implementations, pony have the same size as double and a default- or value-initialized pony doesn't have any bit with indeterminate value. So it's questionable to me whether this example serves its purpose. Would it make more sense to initialize the short member instead?

Start with Note 8 of [atomics.types.operations] and read the surrounding atomic operations wording. Check whether the example demonstrates the intended padding or indeterminate-value behavior, then revise the example if needed; the issue is resolved when the note clearly serves its intended purpose.