Confirmed for 1.14.4 and 19w36a. I really hope this get fixed by 1.15. It's a very nasty one :/
This bug is also present while doing something like /execute store success score @s was_successful run data get entity [<path>]. If no such NBT tag is found, the success stores is 1, while it should be 0.
I attached a world download with the setup used in the video, in case you want to test it.
It takes some time to happen, but It certainly does. I've had it happening several times now. This bug makes it impossible to have a stable Wither rose farm, and any other Wither based farm where you need to keep blocks without blowing them up.
I forgot to specify that. If the block below the mob is not valid for planting the Wither Rose, it would be dropped, and not because of the explosion. That is even with doMobLoot false.
Can confirm in 1.16.4