The block break animation renders at the incorrect rate under (at least) two circumstances:
1: You start breaking the block while in air
2: You change tool during use
To repeat:
1:
Jump
while in air try breaking a block.
The break animation's speed is incorrect
-- View attachment: 'Video1.wmv'
2:
Start breaking a block with your hands
Change item (while still breaking the block)
The block break animation will be incorrect for the new item (resumes with old tool's rate)
-- View attachment: 'Video2.wmv'
This is happening a lot to me as well. I can't believe that there hasn't been a lot of attention brought to it, since I thoughts all Windows 10 version users would see this, but at least there's a report on this.