I know this has been posted here in the discussions before, but there are a lot of new people now and the problem is still happening. It will always happen when there are still uninformed players (which there always will be.)
Please, when you are out mining, if at all possible complete the entire 'rock' and leave an empty space behind. I fairly regularly find places where people have left one-last-bit worth of rock remaining.
They might be doing this because they think they are doing other miners a favor by not 'taking all the rock.' The fact of the matter is, what they are doing is leaving just that one bit for the next miner who comes along, and blocking the regeneration of a full block. If they'd taken it all, there would be a full new chunk re-generated for the next miner.
The only reason for any fully informed miner, who knows how rocks regenerate, to leave 'just one piece' remaining unmined at a location is as an act of aggression against the other miners.