[2.1.12][Linux] Inserter places item on full belt before preceding inserters

[pondohou]

Expected behaviour: The assemblers in a row, the ones placing the objects first would be the ones in the opposite direction of the output belt and onward.
usually the first assemblers in a line "clog up" and idle until more is required on the belt.

But here seemingly, the inserter is putting down science before its preceding assembler/inserter duo, even though both have items to put down.

factoriooddbeltinserter behaviour.mp4

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Things I tried:
I tried removing power, and then giving back power to the assemblers and inserters, problem persisted.
I changed the belts to regular belts instead of undergrounds in front of the inserters, the problem seemed to resolve.
I tried lowering to red belts instead of blue, this made the problem happen but only more sporadically.
I tried exiting to the main menu and going back into the game, problem persisted.

This line is not the only line of assemblers that act this way in my save, its almost every active science line. I think it has something to do with the underground belts but i don't really know.
I'm providing my save game here also, its easier to see this than to describe it.

I find it hard to describe this in text, please help me with the title, Thank you.

[Rseding91]

Thanks for the report however this is not a bug. Transport lines do not have any strict rules about this behavior and inserters may insert items like this at any point on a given transport belt.

[pondohou]

I see, Thank you so much!