Just moved to 3.9.8 and discovered a major safety issue.
If the plane is powered up and the transmitter is in Manual mode with the throttle raised the plane engine will run while motors are disarmed.
The issue is reproducible.
If the throttle is raised slightly the forward flight motor will only turn for an instant but if the throttle is set to full the engine will run for as much 30 seconds!
Immediately on power up the forward flight engine will run at full throttle without arming!