TL;DR
The (new) stack inserter should drop the held spoilable product as soon as the product in hand changes state.What?
The stack inserter will wait to get a full stack (up to 16 items) before making a single swing.An item that is spoilable, can (and will) spoil while stuck in the inserter's hand.
In some unfortunate scenarios, the inserter may be stuck for a very long time (e.g. hours for bioflux), waiting to get enough spoilage to drop anything.