Lets emphasize that a fix can only come from a detailed description of a problem and a successful reproduction in the devs office.
So your question about a fix for the flashing (the other dev still hasn't one, just a workaround) answers itself. Sorry to say that.

I don't have any flashes or crashes, with the cabin on or off, so finding the problem won't be easy as it is system dependent.

Mark, do you know the workaround for that other plane? It is written in their forums and mainly consists of "go to medium detail in the VC".
I know this because I own it too (nice one) and had the flashes there while the 707 is flash-free here.
Their workaround kills the flashes but not the nature of that problem of course.