I don't think that this is a switch problem - if the AP looses the tunnel connection to the controller he'll reboot and start controller discovery from scratch.
It's easy to troubleshoot....
Just configure a SSID on the AP with a bridge@AP topology and a pre-shared key WLAN service.
In the AP proberties go to advanced and enable "Maintain client sessions in event of poll failure".
That will do the following - even if the AP looses the conncetion to the controller NO reboot will performed as the AP has the WPA key stored localy and will still provide service on this SSID.
This option is only used if the AP has a SSID with bridge@AP topology with a WLAN service with either open/none or WPA-PSK because this two don't need the controller to allow clients to connect as open/none has no key and for PSK the key is stored in the AP.