XPUB socket not reporting subscribe/unsubscribe only topic

[gustafg]

When a SUB subscribes or unsubscribes to an XPUB there shall if verbosity is set to 'allSubsUnsubs' be generated a receivable message on the XPUB socket telling us if what happened was a subscribe or unsubscribe event and the topic involved. With 6.0.0-beta.16 only the topic is reported unless I am doing something stupid in which case I would be grateful to be notified as to how to perform the call to get the subscription bit out of the message.

See last value caching proxy here for example on how I expect it to work:
https://zguide.zeromq.org/docs/chapter5/