Rodrigo,
Aplique o Rollup conforme artigo abaixo nos servidores DHCP e faça um novo teste.
Veja que ele explica problemas com o DHCP / Failover / Reservation e sintomas similares ao seu.
http://blogs.technet.com/b/teamdhcp/archive/2014/02/26/dhcp-failover-patch-to-address-a-reservation-issue-and-another-issue-related-to-failover-partner-not-accepting-state-transition-from-bad-address-gt-active-has-been-released.aspx
Obs: O Rollup para Windows Server 2012 R2 é este:
https://support.microsoft.com/kb/2919355?wa=wsignin1.0
Att.
Carlos Eduardo Gnochi de Oliveira