Gavin,
I was part of the BI 4.2.3 Beta/Ramp-up testing team and can confirm this is a known BUG. I have received confirmation of the KB Note that will be coming out in the future.
This is a BI 4.2.3 Platform BUG for sure, is will get resolved in Patch 1. I will try to get more information.
Regards,
Ajay