How do you clear a GCS failsafe?

I’m using SITL and have successfully created a GCS failsafe and watched my drone do RTL.

Unfortunately I cannot get my drone to change out of RTL mode (either using Mavlink or using the SITL commands), and I get the statustext “PreArm: GCS failsafe on” from my drone.

Does anyone know how to reset a GCS failsafe?

At present I just reboot Arducopter but this seems overkill. Thanks.