Orbit mode testing failed V1.9.0


First I would like to thank you for the work that contributing orbit mode. It is a great feature.

Week ago I started to test the Orbit mode, but no luck so far. My drone setup:

Airframe: Generic-Quad-X, 450
FCU: MindPX V2
Firmware: PX4 V1.9.0-beta3
Estimator: LPE

The quad can fly Goto mode and Mission mode quite flawlessly.
When I command ‘orbit mode’ from QGC, the quad behaves pretty much the same every time: it first fly a straight line to get onto the planned orbit, and then looks like start orbiting but slowly descend down itself to the ground.
Below is the flight log from one of the test flights. In this flight the quad automatically climb up and return to home after descend from the orbit and almost touching the ground, but I am not quite sure what triggered this return to home fail-safe.

flight log

Do i still need any precedence setup to orbiting successfully? Do you think anything I may miss?

I also attached the flight video so you can have a direct impression on what’s happening.
flight video


I checked the v1.9 change list, the orbit mode is not listed. However check into the source code the logic did present.

So I am confused is orbit mode supported in V1.9 or not? Is it suppose to work?