I don't know if this issue have its place here or if it has already been reported, but when you grow a dark oak near the bedrock, some bedrock blocks may be replaced by dark oak logs, so that you can enter the Void in survival mode. Bedrock shouldn't be broken.

How to reproduce:

• Create a New World
• Reach the bedrock
• Place 4 dirt blocks on the bedrock
• Create a Dark Oak tree (4 saplings in 2x2 square)
• Use Bone Meal on one of the saplings

Here's a video:
http://www.youtube.com/watch?v=DH4H8ldQGEo