Cisco Wireless :: AP1142 Preferring DHCP Address Over Static Configuration

I'm experimenting a strage issue with some AP1142 that prefer getting new IP from DHCP server rather than using the static ip already configured.
 
I've got  more than a hundred of 1142 APs already conected to a 5508, all with static IP, all working fine for about a year.
 
As i installed 30 more AP, i enabled a dhcp scope on the controller to give IP to the new APs and when the new aps got registered i changed the configuration to static IP.
 
The problem comes when some of the older AP than have already static ip are gettig ip from dhcp scope.
 
If i look at my WCS, it reports that this APS are getting DHCP IP because they cannot reach the controller with their static ip. As this is impossible, because the static ip and the dhcp enable scope are in the same subnet in a layer 2 configuration and with the same gateway. (e.g: old AP 10.10.2.10/16; new AP(dhcp 10.10.3.10-50) 10.10.3.15/16; gw 10.10.254.1)
 
The problem comes when i disable the dhcp scope, all the older aps that got dchp ip from the wlc scope instead of using their staic configured ip are deregistered. If i reset every ap manually, from the swithc disabling PoE, they start to use the static ip and everything comes fine.
 
This is happening with about ten of fifteen APs from the 100 installed, that is the strange thing because this seem to be very random as the failing APs are installed in different building and connected to different switches.
 
As now i have disabled dhcp scope and all APs (old and new) have static ip everything is ok, but i will have to add some more APs shortly and every time i enable the dhcp scope on the wlc