Video tracks stacking in reverse? Obscure setting or error?

Hey all,

I've seen a lot of errors and weird behaviour over the years in Premiere but this one's new to me.
The video attached shows the problem, it seems to be rendering the video layers in reverse order. So My V1 track is rendering on top of V2 and so on. I'm dragging my background clip up to V5 (Which appears behind V2) while i edit for now but it's incredibly frustrating and counterintuative. It's only doing it on a handful of sequences so far.

So far I've tried copying to a fresh sequence, updated Premiere, updated graphics, restarted etc. 

Any advice would be appreciated

https://youtu.be/Do7eAMxE3PY