When mining a 1x3(tall) tunnel then digging walls for the minerals blocks are going though solid blocks above to the surface. I have added a few screen shots of this after i noticed i lost a few diamond ore, then i found a line of entity blocks corresponding to my mine below.
The two desert pictures are of the same location. second with F3 active.
Duplicate of MC-47650 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.