Vines can be placed invisibly under leaf blocks

^{Update by [Mojang] Mega_Spud (Jay Wells):}
Verification Builds:
1.2.6.2, 1.2.5.52 Retail

Summary:
Vines can be placed in a one-block space underneath leaf blocks, and will be invisible.

Steps to Reproduce:

1. Stack two leaf blocks on the ground
2. Break the lower leaf block
3. Place a vine underneath the remaining leaf block

Observed Results:
An invisible vine block will be placed underneath the leaf block.

Expected Results:
Vines shouldn't be able to be placed underneath blocks, and they should never be invisible.

Screenshots/Videos attached: Yes

Notes:

---

Original Description:
Ivy invisible when it is laying on the ground in contact with a leaf of tree

To reproduce the bug, plant a tree (example oak) then give it bone powder then put ivy on the lower leaf (s) to a block of soil (Important !!) then put on floor .

Possibility to put under all the leaves has a block of the soil.