Cannot swap a V4 and V3 function deployed in separate staging slots

We are looking to upgrade from V3 to V4 functions and ran into an issue when testing a deployment out.

We have a V3 function deployed with staging slots currently. We deployed the V4 function to the staging slot which contained a V3 function which worked. When we swapped the functions we are receiving a 400 back and could not complete the operation. As soon as we set the "production" staging slot's runtime to ~4 the swap completed just fine.

I then went ahead and created a sample function to test this out a bit further. I created a V4 & V3 sample function. I deployed the V3 function to staging and prod slots and they worked just fine. I then deployed the V4 function to the staging slot where the V3 function was. Then we swapped the slots and operation succeeded but resulted in a broken function. The FUNCTIONS_EXTENSION_VERSION was not swapped causing the function to break. As soon as I updated the version from 3 to 4 the app started working.

I then went ahead and attempted to implement the "fix" based on recommendation from #925 by setting WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS to 1. This also did not end up working, I even attempted to set the setting as a deployment slot setting which did not work.

What issues do I have?
- Cannot swap a V3 and V4 function
- Swapping a V3 and V4 function doesn't respect the FUNCTIONS_EXTENSION_VERSION even after setting WEBSITE_OVERRIDE_STICKY_EXTENSION_VERSIONS to 1