I am using a GL-AR300M in Client and AP Mode(Master).
Sometimes the wifi in client-mode disables itself for no reason, while the AP-mode is still enabled.
I tried to use watchcat to force a reboot when the GLAr300m cant ping to googles server, but even after a reboot the wifi in client-mode is still disabled.
Basically it is working as a forwarder and if the client part fails to connect/authenticate to the remote ap then there is nothing to forward so the ap wireless is switched off.
If you want it to stay on all the time try configuring as client/ap(wds) instead. This means the local ap will set up to forward itself downstream using wds and therefore be abailable at all times with the client part picking up the remote ap if available.
In the default firmware there is a repeater manager watching the connection. If the client is not stable for several times, the router will disable the sta so that AP will be enable without problem.
In /etc/rc.local, the repeater manager (gl_health) is started each reboot. It will also start if you change sta settings.
To disable this, change /usr/bin/gl_health to another name