ok, I definitely see what you are talking about... it looks (to me) like it is adjusting the global layer - stretching it out to compensate for the shrunken layers, and there is a split second when there is nothing to display around the edges of the background sprite.
so, I tried over-sizing the background sprite way beyond the edges of the HUD layout and that seemed to help a little (not completely but was noticeably better). then I tried making new background layers on all the layouts (kind of defeats the purpose of a global layer). But that didn't really help. I also tried putting a wait 0 before you change the scale at start of layout to make that the last thing it does on the current tick - hoping that the global layer would get in place first. But that still didn't solve the problem and then you could see things snapping to their new size.
so, I don't think there is anything else you can do. Over-sizing the background image gave the best result. You might want to file a bug report to have Ashley see if there is anything he can do about it.