As often happens in the Linux world, dhclient evolved to become more RFC compliant which can break software which is decidedly less so, e.g., your Microsoft DHCP service. You have two options:
1) Modify your Windows DHCP server and set aside a DHCP reservation according to the overblown MAC size address that appears in the lease entry. The downside to this approach is that it requires you to have change access to this server and the fix is a bit of a kludgey workaround as the overblown address may change as it is a superset of the actual 6 octet hardware address of your host.
2) The better option is to create (as root) an /etc/dhcp/dhclient.conf file (it probably won't exist in F21/22) on your Linux client with the following line:
send dhcp-client-identifier = hardware;
This line was present in Fedora versions prior to F21 but was removed when dhclient became RFC 4361-compliant. To make it work with older DHCP servers, this explicit line will cause the exact MAC address to be issued to the DHCP server rather than the server extracting it from the chaddr field of the DHCP packet.
Hope this works for you...and I hope you continue to stick with Fedora as it is a great operating system. If you are curious about this issue, you can find more info here