named-checkzone complains about MX records

Summary

The tool named-checkzone complains about MX records being CNAMEs, even if they aren't CNAMEs

Steps to reproduce

Just check the zone gitea.de:

named-checkzone gitea.de gitea.de.zone

What is the current bug behavior?

Error message:

zone gitea.de/IN: gitea.de/MX 'mail.misterunknown.de' (out of zone) is a CNAME 'mail.misterunknown.de.' (illegal)
zone gitea.de/IN: gitea.de/MX 'mail2.misterunknown.de' (out of zone) is a CNAME 'mail2.misterunknown.de.' (illegal)

What is the expected correct behavior?

No error messages.

Relevant configuration files

• gitea.de.zone => https://pastebin.com/8caXrx9L

Relevant logs and/or screenshots

# named-checkzone gitea.de gitea.de.zone 
zone gitea.de/IN: gitea.de/MX 'mail.misterunknown.de' (out of zone) is a CNAME 'mail.misterunknown.de.' (illegal)
zone gitea.de/IN: gitea.de/MX 'mail2.misterunknown.de' (out of zone) is a CNAME 'mail2.misterunknown.de.' (illegal)
zone gitea.de/IN: loaded serial 2018062100
OK

Possible fixes

No idea.