Let's set some terminology:
Block A is a solid opaque block (such as stone.)
Block B is a block that breaks instantly (like redstone or a sapling.)
If Block A is being pushed by a piston into Block B but Block B is broken the exact time this happens, Block A will be destroyed instantly and will not drop, and Block B will drop.
Cleaning up old tickets: This ticket has not been updated recently (~1 year+) so is being closed as Cannot Reproduce. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines.
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