The past few updates ive been able to ealk through blocks. It started about a month and a half ago, I would be able to go through halfslabs if they were one full block off the ground. It would stick for a second then i could walk out. Then it started happening with solid blocks (leaves, planks, stone, and fences and glass panes to name a few i noticed first) as long as there was an open block under it. Now i phase through solid walls if i scooch into them or jump into them. Its not a full xray mode thing, i just see the inside of the block and the edges are clipped through so i can see the sky but not caves. It cant always happen, i usually can do it underground but never above ground. Its really freaking me out and none of the updates seem to make it better. I can take pictures of the screen with my phone if needed.  My world is NOT using experimental gameplay it is fully vanilla and just about 9 months old.