I created the Wither in survival in a cave system.  It does the initial explosion when generated and breaks surrounding blocks.  Then it rises and stops at the cave ceiling and just hangs out there.  It shoots the skulls but is stationary.  Once I get it to half strength, it falls to player level and flys, but it doesn't break any blocks.   It still shoots the skulls, but wont fly into the cave wall destroying blocks like it used to.  It drops the star when defeated.  But I use the wither to break hundreds of blocks for me so I dont have to mine them.  Since the 1.8.0 update, it seems to have gotten lazy.  I want to be lazy.