the answer is easy but maybe satisfying. It is correct that if you add multiple episodes to a post, only one episode per post will be in the RSS Feeds. The problem is that it is not recommended to have more than one enclosure/attachment to a post in RSS Feeds. iTunes for instance does not support multiple episodes per posts. In the podPress FAQs are two links which will lead you to a more elaborate and complete explanation.
On the other hand it is only a problem of the RSS specification. The same posts in an ATOM feed should have all episodes.
But if you (your client) want to use the iTunes podcast repository to distribute the episode one will have the same problem again.