A flash in a transition

There is an annoying flash in a transition if I have “Include background in transition” NOT CHECKED.

A demonstration is here:

removed link

Until I figured out a workaround, it meant that any transition that has movement, such as Center Seam Tilt – Bottom, could not be used. (For such transitions to work properly, Include must not be checked.) I was limited to transitions such as Blend. This was a deal-breaker until I devised a workaround. It seems it flashes when it is transitioning from the show background of slide 1 to the show background of slide 2.

I got around it by adding a slide background (identical to the show background) to each slide. That way I can have Include not checked. Presumably, the flash still happens, but it is covered up by the slide backgrounds.

I am using Photopia Creator version 2.1.1077.