In version 2.8.27, when setting the state of a static dhcp lease from enabled to disabled, the client who’s MAC is associated to that lease can no longer get any IP leases from the dhcp server.
Under the leases, status for the disabled lease still says “waiting”.
Is this a bug or a feature? I don’t see this mentioned in the manual.
I ahve similar problem. When I use DHCP from ip pool it works ok, but when I add specific MAC to static lease it cannot get DHCP info.
It may be related with MAC forwarding problem I noticed using Ovislink WL1120AP as an wireless client.
in 2.8 disabled leases are considered as clients who are not permitted to receive an IP. some will consider it as a bug, others as a feature 
in 2.9 it works differently, the disabled leases are treated the same as they wouldn’t be there at all. if you want to disallow the client to get an IP, you should set block-access to true