Are underscores no longer supported in Bind 9.4?

[Jake Morrisey]

Does bind 9.4 no longer support underscores (_) in the A records?
I know I have these in many records in versions before 9.4.
Here is the error that I am getting now.

Feb 28 18:29:54 t141 named[8767]: db.example.com:77:
test_underscore.example.com: bad owner name (check-names)

As soon as I remove the A record with the underscore it in, everything is
fine and the zone loads.

Is this a new rule / RFC?

Thanks,
-Jake