I have noticed that before, and have been trying to figure out how and why those lens distortions exist. Obviously, it's not a tilt shift lens.
And sorry, I've been low on updates. The depth map creation is a time-consuming process, especially when this is the first project you are doing it on.
The nice thing is that with a depth map I can add shallower depth of field to many shots and maybe like in the above example above, have it more prevalent on the top and bottom.