There's an inconsistency in Minecraft that's been bugging me recently. In fact, I've come to the conclusion that it is a bug. The problem is that vines block tree growth. Let me spell out some details in Q&A format:
What does "blocking tree growth" even mean?
If you attempt to grow a sapling while a it is blocked, it will never grow. A sapling is blocked from growing when blocks of certain types are in a location that it would occupy if it grew. Exactly where these blocks need to be placed to block tree growth varies greatly and is beyond the scope of this summary, but suffice it to say that if one of these growth-blocking blocks is placed directly above any sapling it will never grow.
Which blocks block tree growth?
Wood and leaves, which are generated on all trees, do not block tree growth, meaning you can grow trees through most other trees. Most solid blocks - like cobblestone, dirt, and wood planks - do block tree growth, meaning trees will not grow through your walls. This is all good so far! The problem is that vines - which cannot be used to build walls and are generated on some trees - block tree growth.
So what if vines block tree growth? The wiki even documents that they do!
I see this as a major inconsistency in the game and a hindrance to creative building.
Why is this inconsistent?
Wood, which is a whole lot more solid than vines, doesn't stop tree growth, while vines do. Furthermore, vines don't block trees from growing at all in real life, while wood might. Imagine if you could grow a real tree right through a log cabin but couldn't grow it through a curtain of vines!
How does this hinder creative building?
Anyone interested in terraforming a jungle has likely run into this issue as jungles are rife with vines and trees. I'm sure quite a few people have been confused about why their tree won't grow when the answer is the vine hanging down above it! Furthermore, this throws a huge damper on anyone who wants to grow stuff with large jungle trees as vines are generated whenever you grow one. If you wish to grow a jungle tree near another jungle you have to first shave off all the vines!