Factorio Forums

The left lab has +250% speed, the right lab has +2000% speed. Both labs are being fed by a stack size 1 inserter.
The labs are off due to not having all packs for the tech picked.

Both labs stop being fed when there are 2 packs. In most cases this is fine, but it can cause issues with chained labs with high speed and therefore limits design options.

If I replace the labs with mk3 assemblers (filling the right one with speed 3 modules) and set the recipe to green circuits, the left one fills to 4 iron and the right one fills to 22 iron.

Thanks for the report. I don't consider this a bug as much as a not-implemented feature for labs. The fact that it makes chaining labs not the perfect solution every time is kind of a nice trade-off. It means you have to decide if you want the ease of chaining labs or you want maximum speed.