BIND started replying to queries for .com with .COM

Tue Mar 29 22:04:34 UTC 2016

I rebooted one of our BIND VMs this morning. It's running BIND 9.10.3-P3. We
noticed that queries for domains with domain.com were answered with
domain.COM with the .COM in capital letters. Other high-levels like .org
were not changed. It caused a monitoring probe to complain because it wasn't
getting back what it asked for.

Restarting bind on this server fixed the problem. Any ideas on what
happened, or where to look?