This bug duplicates any block attached to a slimeblock. To reprodude this bug you must first have 1 slimeblock, 1 restone block, 1 sticky piston and several blocks to duplicate.

1. Place the piston facing up.
2. Place slimeblock on top of the piston.
3. Place the other blocks around the slimeblock.
4. (creative mode) Now place the redstone block beside the piston and quickly destroy it, repeat this process quickly and you will have the blocks duplicate like the photos.

Doesn't work with clocks.