I saw that ticket before posting this, however to me it seems different. In that example the first hopper gets filled up by items, that's why it can push items into the top chest while simultaneously the hopper below pulls items. However in my case if you see it, in the hopper above the first chest there's only one item at a time and that is why it's odd to me. The only way I could explain this behavior is if one of the hoppers (probably the last one under the furnace) would push items at a speed greater than standard hopper speed. Basically if every hopper under the furnaces would work at hopper speed maybe the items sometimes would pile up under one of the furnaces temporarily but even if it's at the last furnace hopper, that hopper should push items at standard hopper speed only, that's why the next hopper should not split the items, rather sort the items into the first chest. I can accept the judgement if you say this is working as intended I just wanted to differentiate the problem here so it wouldn't get overlooked!
Furthermore why would the behavior change when replacing one powered rail to a standard rail? It makes no sense.