It doesn't because the last procutivity bonus cycle isn't complete until the next production cycle starts:
![Image](https://forums.factorio.com/images/ext/e92c8d0193a1ff11ec320097d1563ece.png)
In most factories, this is not an issue as they use a continuous production cycle, but I am building a factory that does production in count-exact batches, and this bug makes that impossible.
I'm not entirely sure exactly when and why this happens,but I've observed it in chemical plants and assemblers both. It's possible that assemblers, labs, and the silo are also affected.
Sure way to reproduce:
- place a NEW chemical plant
- give it a supply of petrolium, don't limit this
- give it three prod 3 modules
- feed it 250 coal
Expected: 650 plastic.
Tested with creative mode mod enabled.