Issues with some block loot tables

I've been playing around with loot tables recently and found a potential issue. Trying to replace the vanilla loot table of leaves (specifically oak leaves in this case) doesn't work. I've set the registry name to "blocks/oak_leaves", which should be correct, the namespace is set to "minecraft" and it has the loot table type of "block". Yet, when in-game, it gives normal loot anyway, and ignores my modified loot table. I don't know if this is a bug, or if I'm doing something wrong. If you've got any ideas, please do share.