So, I'm not sure how far back this goes, but steps to repeat:

Summon wolf
use /entitydata @e[type=wolf,r-10] {} to read the current NBTs.
/entitydata @e[type=wolf,r-10]

(Test again to make sure it applied? Good. (Setting it to just 1 won't allow it to function, it'll be the same as 0 or 0b)
Tame it. Now check again. See, how it changed back to 0b?
Now, try running the command to put it back. It won't work.

I haven't even begun to start testing to see what else would change and lock yet, nor gone back prior to 1.12.

I'm sure some of you may wonder why even try and enable it if Wolves can't pick up items anyway. Well, they technically can in the same way you can equip a Villager: using Dispensers. But, only if the CanPickUpLoot tag is set to true.