Steps to reproduce:

1. Create hostgroup with minimal 2 hosts. One with a tag and tagvalue
2. Create maintenance period with match on hostgroup and tag name + value
3. Browse to monitoring - Hosts, all hosts are displaying maintenance, also the hosts without a tag and value.

Issue is only cosmetic, maintenance period works correct, trigger fires for hosts without tag or different tag.

Result:
See screenshot...
Expected:
Not displaying maintenance for hosts without matching tag.