Lucatec® Mask can currently not move sent messages when this option is enabled as it relies on messages being stored into the primary user's Sent Items folder. All Outlook options that prevent this (another example would be the explicit Save sent message to option on Outlook's Message Options dialog) will stop Lucatec® Mask from moving or copying sent messages to the desired location.
However, as of version 2.2.2 Lucatec® Mask implements its own version of this option which we encourage you to use instead. It also has the benefit over the built-in option of working inside Public Folders, too. It is labelled "In folders other than Inboxes, save replies with original message".