Friendica with AP support receives duplicate messages from Hubzilla
There is no way for Friendica to know that a Hubzilla Diaspora message and a Hubzilla AP message are one and the same, so when it receives messages over both protocols, it can result in duplicates on the Friendica timeline.
It seems that the solution requires assistance on the Hubzilla side. When Friendica talks AP to itself, it includes the GUID in an extended field. This gives it the chance to deduplicate the same message received over DFRN, Diaspora and AP.
Original issue: https://github.com/friendica/friendica/issues/6068
 actually, is? :-)