Bug itself:
When breaking a 2-block-long item, such as a door, bed, or a sunflower/rose bush, it gives you 2 of the same items. 

Recreate it: 
Place a bed, and brake the top part. It'll drop 2 beds.
Place a door or flower, break the bottom. You'll get 2 of those items.
(Video here: https://youtu.be/V09c7y995HQ)