I noticed that the textures for vines were inconsistent. If you place a vine on a block which forms a corner with another block, the vine only shows up on one side (shown in attachments).

Steps to Duplicate: (Detailed in 3rd and 4th attachments)
1. Place two blocks diagonally from each other.
2. Make each stack two tall.
3. Place a vine on one of the upper blocks.
4. Place another vine in the same inside corner on the other block.
5. Wait for the vine on top to grow down.