Closely relates to MC-206615, which is the bug that allows this effect to be seen.

Note how in the first screenshot, the collision box of the dripstone clearly extends over three powder snow blocks. Yet if any regions of the powder snow overlapped by the hitbox are targeted, the powder snow is the block that ends up getting targeted, even though it should be the dripstone.

This is due to the targeting hitbox, unlike the collision box or model, not being allowed to extend outside of the block it exists in, which is itself inconsistent.

I'd advise fixing the fact that targeting hitboxes can't be targeted if they extend out of the block they belong to, rather than just not allowing stalactites to extend out of their block.

I've been able to see this behaviour as far back as Beta 1.2 with glitched overeaten cakes with beds, as well as in Beta 1.8 and up with overgrown seed stems (before both were removed in 1.8), but this is a legitimate way to see this effect.

This bug also affects pistons - see MC-124459