The bug that has been persisting since Build 11 I believe is still existing.

I noticed when mining with my iron pickaxe, it seems like I'm mining with efficiency every time.
There have been instances when I've broke stone in a second
and obsidian with a diamond pick only takes like 3 seconds.

I think this happens when you hold on something but don't break it and then move to another block which breaks it nearly instantly.

If it helps, it is shown and mentioned in YouTuber JackFrostMiner's video: http://www.youtube.com/watch?v=KobyYEHgOqU

Device: Nvidia Shield Tabelt