isc-bind-esv Repository - "yum update" doing undesirable things!

[Matthew Richardson]

I have been using the isc-bind-esv repository on Centos 7 since it was
created.  On each upgrade, a "yum update" has done the correct thing by
upgrading from the running version to the latest version.

Today (happily on a cloned test server!) I repeated this with the upgrade
being from 9.11.6 to 9.11.6.P1-1.2.el7.

It seems that the package names have changed and that Bind is now installed
in a new directory structure below /opt/isc.  In my case, a previously
working authoratitive configuration is now comprehensively broken.

Before troubleshooting, I was wondering whether I had missed any release
notes or similar which might explain what is going on.

Best wishes,
Matthew