I have a setup with a requester station that deliberately doesn't have enough inventory to unload a full train. (It's requesting coal into a chest limited to 10 slots. This is for a refuel station; I'll want to upgrade my train fuel to solid fuel/rocket fuel/nuclear fuel in turn, so I didn't want to have much fuel at each station to empty out.) Following the Quick Start Guide, I just added a provider "Station" next to the coal train stop, and a requester "Station" next to the fuel train stop. The requester also has a constant combinator with coal=-450 and "request threshold"=200.

However, this doesn't work; the train schedule for the provider stop wanted coal>=450 AND idle for 1 second. I didn't bother putting a limit on
the train loading (because the Quick Start Guide didn't say it was necessary), so the train was never idle; it filled up, and then got stuck trying to unload 4 wagons full of coal into 10 slots of a chest.

I'm not sure if this is a bug in the mod or if it's working as intended. If this is intended behavior, maybe fix the Quick Start Guide? Something like: "Note that the basic provider station described here may over-fill trains; please ensure that the requester station always has enough free space to unload a full train, or use the output of the cybernetic combinator to stop loading the train when the requested amount is reached."

Also, there's a minor issue on the mod page: "This combinator can be in one of 4 different possible control modes." Presumably you forgot to change this number to 5 when you added the Fuel loader mode...

I'm pretty sure it's not a bug. Been playing around with the mod since a day or two after release (before the Quick Start guide was on the mod page) and just made the assumption that without circuit conditions, trains will load until full and you want your stations to assume full loads. Hence why the Quick Start guide doesn't go into that, it's meant to be as simple as possible. I do agree that the full-load assumption could be made more explicit (you can see when the trains are loading that the wait conditions are set to "Item Amount" and "1s of inactivity," which is why I assumed the behaviour is intentional).

I'm pretty sure it's not a bug. Been playing around with the mod since a day or two after release (before the Quick Start guide was on the mod page) and just made the assumption that without circuit conditions, trains will load until full and you want your stations to assume full loads. Hence why the Quick Start guide doesn't go into that, it's meant to be as simple as possible. I do agree that the full-load assumption could be made more explicit (as you saw, you can see when the trains are loading that the wait conditions are set to "Item Amount" and "1s of inactivity," which is why I assumed the behaviour is intentional).

Yes this behavior is intentional. I didn't want the guide to be very complex but a quick note to keep stations from having full inventories is a good idea.