UIDropShadowView showing during Flip Horizontal modal transition

I'm attempting to transition from 1 view controller to another, with the illusion that ViewController 1 flipped over to ViewController 2 as a form sheet. However, during the transition, there's a visible gray UIDropShadowView that's ruining the effect.


third from the left:

h ttps://i.stack.imgur.com/84BN4.png


Here's a gif showcasing the problem:

h ttps://i.stack.imgur.com/OEh3P.gif


And lastly, I've attached a Sample Project showcasing the problem:

h ttps://www.dropbox.com/s/lma9lbzdmny2khu/Test.zip?dl=0


What am I doing wrong, or how can I resolve this to create the illusion I'm looking for?

Note: I've confirmed this happens on an actual iPad