When some blocks such as Redstone components, pumpkin and melon are pushed by slime blocks that was pulled by a piston retracting is not dropped any item.
To better understand look at the screenshot. When the lever is deactivated the repeater will be destroyed but will not drop the item.
Attachments
Comments 7

Can confirm this. Tested it in a new world multiple times in Creative and Survival Mode and it happens all the time.
Can confirm this. Tested it in a new world multiple times in Creative and Survival Mode and it happens all the time.