From my reading of RFC4592 I think wildcard A and CNAME records are valid, and my version of BIND (9.4.1) works with them. Webmin doesn't allow you to edit these in the GUI. Is that a bug or is it intentional and I'm missing something?
Webmin should support wildcard records just fine. However, in older releases this wasn't enabled by default ... so if you have upgraded from an old version, you may still have the old setting.
To fix this, edit the file /etc/webmin/bind8/config and change the allow_wild=0 line to allow_wild=1
Yes that was it, I started with it 7 or 8 yrs ago - OK now