Thank you for the clarification.
We have confirmed that this is a defect in the Message Saver. To be exact, Message Saver fails to save a message’s attachments when Ask which attachments should be saved is checked and the message has a Mime.822 attachment. (Support for interactive selection of attachments was overlooked in the processing of such messages.)
Our engineers are working on a solution to this problem and we hope to release an update to the Message Saver Pack by the end of the week.
Once again, thank you for the feedback.