Reproduce:

1. put a insta-mineable block behind any block
   • for the insta-mineable, I tested:
     • potato
     • carrot
     • grass
     • sunflower
     • cornflower
     • every sapling
     • dandelion
     • poppy
     • allium
     • crimson roots
     • warped roots
     • twisting vines
   • for the blocks behind, I tested:
     • tuff
     • stone
     • dripstone block
     • basalt
     • end stone
     • block of amethyst
     • coal ore
     • podzol
     • grass block
2. place your crosshair like in the image pointing to the insta-mineable and the block behind simutaneously
3. make sure, you have nothing in your hand
4. start breaking and release before broken
5. repeat 1-4
6. now the break-animation should still appear on the block behind, even though you released.

I quite often come accross this bug while playing when converting bone meal to carrots or potatos

Edit: I tracked down, where exactly this bug starts happening: In version 1.14-pre6, this bug occurs, in version 1.14-pre5, this bug doesn't occur