Mark; I don't think this has been raised before, but if it has then I apologise...
There is an anomaly in what appears (or more correctly doesn't appear) in the Activity Log, illustrated by this very recent example.
Numbers 1 & 3 above resulted in entries appearing the Activity Log, but numbers 2 and 4 did not.
This seems wrong; should it ever be necessary it is impossible to follow an audit trail where one half of the exchanges are not logged - not even their existence, never mind the content. The "Actions List" includes Messages to +owner but there is nothing listed (as far as I can see) for Messages sent by Owner.
Is this "missing action" deliberate or an oversight? IMHO it would be much better if both sides of any exchange appeared in the Activity Log.