When you swap a block with a leaf block, the leaves start to decay over time, because they are not marked as persistent.

This could be intented behaviour, but I would expect any blocks being placed by the block swapper to act as if they were placed by a player.

This is very much not intended behavior, it's an oversight on my part

almost a year later because I somehow never ended up publishing the file, but this is now fixed in version 2.0