0.16.49 Factory output no longer shared

[Amarula]

What I did:
Factory 1 (producing basic circuits) feeds factory 2 (producing inserters for green science packs) using a fast inserter. Overflow production goes into a chest, using a long handled inserter. (Both factories are assembling machine 2. No control circuits, no bonuses, this is at the start of a new game.)

What I expected:
I expected production would be shared between the two inserters taking output from factory 1; one circuit would go to factory 2, and the next would go to the chest (assuming factory 2 needs a circuit, and assuming there is room in the chest). According to the wiki "the inserter who can grab the items the fastest will grab them first," so I would expect if anything the fast inserter would have a slight edge over the long inserter. Note that the wiki doesn't actually go into any details of using inserters to remove production output from a factory, it discusses using inserters with belts, chests and trains. I have done this prior to 0.16.48 with no issues - factory 2 might be slowed down a touch but not completely starved. Many designs rely on shared output, for example three cable factories feeding two basic green circuit factories.

What happened:
All the production went into the chest, no circuits made it to factory 2, so factory 2 stopped producing inserters.

[DaveMcW]

If both inserters are idle, inserter speed doesn't matter. The tie is broken by build order.

An easy solution is to put the overflow chest between the two assembling machines.

[bobucles]

I just tried it and the inserters still take turns. Is something else happening? If one assembler is stalled it obviously won't accept any more input.

[Amarula]

I do have a similar setup that is working: one gear factory feeding both the inserter factory and a belt factory, and overflow going into a chest. Inserters and belts both get built to feed the green science pack factory, at the same time that the gears chest is getting filled as I grab components to build more stuff.
Clearly there must be some difference with the circuit factory: go back and unlimit the circuit chest so there is lots of room, the inserter factory has iron plates and gears, and is waiting on circuits, so both are ready to accept circuits from the circuit factory. And the production continues to be directed entirely to the chest.
Dave, I am not sure what you mean by build order breaking the tie... I have tried removing and replacing both inserters, and the chest, and the factories, and still all the production is going into the chest.
And yes it is easy enough to put the overflow chest between the circuit factory and the inserter factory, I am just curious as to what has changed because it used to work (I used a blueprint I have used in other games).
Thanks all for taking the time to respond.

[Amarula]

A little more experimenting: it looks like the circuit factory was waiting on cables; change from one inserter feeding cables to three, and it is back to working, with output shared between the factory and the chest. I am still very curious to know what changed but I don't need to re-arrange my factory to make it work.