Note that adding only one buffer slot will only help if you have a single mixed-quality science.

Otherwise, let's say you have red and green, each in normal and uncommon. Whichever kind of red science arrives first, normal or uncommon, will get put in the red slot, while whichever kind of green ...

TL;DR
Add additional "buffer" slot to labs so that when using input science packs of variable quality labs will not stutter.

What?
Add an additional slot to labs to labs for a small buffer of mixed quality science packs.

It could work like the heating tower does where there are two slots for ...