Blocks taking multiple attempts to clear

What I expected to happen was...:
after clearing a block, it pops out and is collected.

What actually happened was...:
block did not clear, it resolidified and had to reclear from 1-3 times before block would "pop' out and be collected.

Steps to Reproduce:
1. just mine a ton of blocks it happens infrequently but out of around 64x27 it happened approxamately 15 times from only having to clear it one more time, up to 3 more times.
2. ...
3. ...