Conduits, kelp, coral (fans), and tall grass have full hitboxes

The hit boxes look smaller now, but you can still hit the full cube to destroy them.

Still happening in 1.13-pre1.

I'd also like to add that this bug doesn't affect only the blocks mentioned here; it affects ALL waterloggable blocks that have water in them. Aiming at the water source that the block is in makes the game think you're aiming at the block's hitbox, even if you're not. Came across this bug just a bit ago when I noticed the game was forcing me to target a sign when I was trying to test a different bug.

Relates to MC-4090 and MC-129205

I would say that the hitbox tag already says that. And it's used by 172 reports, the two you listed don't seem to be too much more related to this than the other 169.

Still able to reproduce in 1.13-pre6 using 2tall grass and flowers.

BBs of blocks listed in description were adjusted in 18w20b. Bug was later reopened due to MC-130554 (BB was defined correctly, but block picking used bigger box), which was also fixed.

Mismatched hitbox on double grass and flowers is separate issue (especially since they can't be waterlogged) and does not warrant reopening of this bug.

Note: also, this had no connection to MC-128311 and MC-128393 mentioned in description, since that is determined by separate value.

Confirmed, the hitboxes are correct in 1.13-pre6.