I know that this is actually intended and it was specified on the changelog, but I think that this isn't really a good change. It takes a lot of risks to get your hands on a lot of wither roses. In example, before 20w19a released I've just made a wither rose farm in my snapshot survival world. I struggled 6 hours on it and my wither eventually escaped, so it wasn't all nice and easy.

Now, I'm not saying that this is the reason why I think this is a bad change. But this "bug" fix has broken a lot of farms that weren't possible before. And yes, we can totally make our way around all of this changes. But, in a way, Minecraft is a game about endless possibilities, about having at least 5 ways to achieve the same thing. And removing one of the best features for the mob-farming redstone community is diminishing the number of ways you can farm mobs.