Hitting the bottom block of a tall flower with a deployer holding shears drops the item on the ground and also collects it in the deployer, duplicating the flower.
Hitting the top block doesn't duplicate it: the block is dropped but not collected by the deployer.

The tests below use botania tall flowers but I've also tested vanilla's rose bush and got the same results.

This also seems to occur when deployers destroy the upper half of a door or the foot of a bed.
EDIT: My mistake, it doesn't actually duplicate the doors or bed in this case, just drops the item without collecting into the deployer.