When attempting to Copy+Paste a certain pickup and drop configuration onto an already existing Inserter it won't pick up items, only after opening the GUI and clicking on the desired pickup position (the GUI marker is already at the position, you kinda "confirm" it by clicking it again) will it begin to pick up stuff from a belt.
Noticed this when building a long line of identical assemblers, placing all Inserters in default position and then configuring one and attempting to paste it into the rest.
