MUC-PMs: add <x/> tag when sending them
A recent change to XEP-0045 §7.5 added this passage:
To allow for proper synchronization of these messages to the user's other clients by Message Carbons (XEP-0280) [19], the sending client SHOULD add an element qualified by the 'http://jabber.org/protocol/muc#user' namespace to the message.
Please implement this, so that other clients can properly detect Carbonated and MAMified PMs.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information