Hoppers ignoring GUI max stack limit

Whenever I have a hopper going in to a block with a GUI bound to it, it ignores the Max Stack Size of the GUI, it will keep filling without any way to stop it.

(Example)

64 logs in a hopper

Max Stack Size of slot is set to 10

Hopper puts 64 logs into a slot with a Max Stack Size of 10.

I've spent the past 4 hours trying to fix it using the condition tab, but it also seems to ignore that too...