The explosion the Wither makes upon spawning can break Obsidian at point blank range. Not sure if intentional, wasn't happening in 1.4.2 pre-release
Linked issues
duplicates 1
Comments 4
Please edit your summary to something more descriptive. "Blast Resistence" in itself is not a bug, you may want to change it to something like "Wither blows up obsidian when spawned" if you believe that is the bug.
If the Wither has no targets, it shoots out blue skulls which can destroy almost any block. So if you trap it, it WILL break out.
Duplicate of MC-410, which is marked Works As Intended.
This is an intentional feature of the Wither boss. On his initial explosion, he will destroy every type of block except for bedrock and anvils (from what I've witnessed). After the Wither starts shooting, every block except for bedrock has the possibility of being destroyed.
[Edit] Actually I just ran 3 tests and the initial explosion did not break the obsidian. Only when he started firing did it break. If he is in a tight enclosed space, he will explode and then almost immediately start firing it seems, so it may appear that the first explosion is doing the destruction, when it isn't?