When digging out blocks, the textures do not change immediately when the block is removed. Also when blocks are placed. Attached is a series of screenshots which show digging straight down a few blocks, and the effect is X-ray. If not over the standing over the hole, the hole is not seen. The last screen shot shows placing a block, and only the outline is seen.

All of these visual bugs eventually correct themselves. I'm not sure what triggers the correction.