Deep frozen ocean biome does not generate with ice on the surface

Deep Frozen Ocean biome is not generating ice blocks on the surface, unlike shallow Frozen Ocean does. If the generation of an ice patch in a shallow Frozen Ocean attempts to enter the deep biome, it will be just cut, like if entered in warmer water.

Shots 5 and 4: same seed (pollinating sandboxes), same coordinates (0 128 0 0 90), but deep frozen ocean buffet in shot 5 and shallow frozen ocean in shot 4.

Shots 3, 2 and 1: an example in a default world. Shot 1 shows frozen ocean at left and deep frozen ocean at right. Shots 2 and 3 show the two sides of the biome border, at the same location.