Smite 4 enchant significantly nerf Looting 3 bonus

Firstly I got suspicious when, after killing 60-70 Wither Skeleton in my Survival World, I recived no wither skull at all after installing the 1.4.4 Pre-Release patch.

To reproduce the bug I then did some test in creative mode spawning serveral Wither Skeleton and that's what I found out:

Using a diamond sword with Sharpness 4 dropped a consistent amount of wither skulls (like 2 for 50 skeletons)
Using a diamnod sword with Sharpness 4 and Looting 3 greatly increased the amount of skulls dropped (like 4 for 50 skeletons)
Using a diamond sword with Smite 4 and Looting 3, however, did show a strange behavior: in several try I recived an incredibly low amount of wither skulls, even less than the one expected with a sword with no looting enchantment (like 1 or even none for 50 skeletons).

Unfortunatly I'm not able to do more precise testing, I hope this is enough to allow further investigations.