About that pop … my guess is this initially came from some lenses with a wavy focus plane, so not a plane at all. Especially some of the older M-mounts were designed that way. Which fits nicely, because if you would look down on the area in focus it would be an M or W depending on the direction. Modern lenses give in to the wall-testing crowd and are more like a dash — super flat.
If you use such a lens at its widest aperture(s) the transitions between in focus and out of focus create this strong 3D effect because they emphasize the depth of any object.
Since those old lenses are usually a lot softer than modern day creations this effect does not look bad but rather nice and interesting.
At least that is my verdict from testing and using various generations of (mostly Nikon) lenses and reading a lot of the lens tests by Roger Cicala — the mythbuster of photography.