Interesting problem. But ofcourse if you really need a powerbox to get the camera working I wil say the Flycam guys really have a bad design.
It can make sense that it doesn't work on Fasst but when you have also tried the 9C i will say the design is bad. This should be compatible with most rc stuff. You could for a test try channel 9 on the 35 Mhz receiver with the 9C. This is a on/off channel and not proposional. It may make a difference.