this is an old issue but if any one has this problem too, it can help:
For instant controller there is no problem as the other friends told.
but in CAP (Controller Based Access Points) you have to do the following configs.
(These configurations WON'T work with 802.1x Authentication only works with psk (preshared key)).
you have to use preshared key example: wpa2 aes with preshared key or wpa etc... for your ssid
1) Configuration > AP configuration > (ap group you use) (default for me) > Wireless Lan > Virtual AP > (your ssid profile)-vap_prof test-vap_prof (for me) > (switch to Advanced manu tab)
in Advanced menu ;
a) forward mode : Bridge
b)Remote-AP Operation : Always
than apply & save your config
After all if you do the config like this,if you have a single controller without a backup controller and when your mobility controller stops working or electricty problem or etc.. your AP's will be still working + if you unplug and re-plug electric cable of the AP. it will boot up and you can use your AP too without controller. (my APs were iap and i converted them to CAP mode for these Demo Labs)
This scenario works for me fine. I hope it works for your screnario too