Flix and SBpro prob

Using 5.5 SBPRo and Imac. I have selected a grey default Bg for my panels. When I export to Flix this grey Bg default is not exported along with each panel . I have to manually add a grey bg layer to each panel to get this grey bg on to flix.

Its wasting a lot of time as i can’t automate the process because i have camera repositions which mean the grey Layer doesn’t always fill the camera field and I have to manually adjust the layer to fit .
Any ideas or is this just a bug that needs fixing ?

Any help appreciated.