[kovarex] [1.1.53] Splitter with input priority leak from low priority belt when first connected

[esn]

I have two belts and a splitter with an input priority (no output priority).

factorio_vx43XFAqP1.png (322.29 KiB) Viewed 1353 times

The belt with the input priority is filled first.
Then the second belt is filled.
What will happen is that two items from the top belt (without input priority) will leak through the splitter although the bottom belt is always full.

factorio_gif_bug_report.gif (2.52 MiB) Viewed 1353 times

[boskid]

I am going to move this to Not a bug. This specific behavior happens because splitter in order to not take from the secondary input needs an item in the internal buffer located on the priority input which holds roughly 1 item on each priority lane. Because the output was never blocked, when item is moved from the priority input to the output in the next tick the splitter sees no items on the priority input but there is an item on secondary input so it tries to transfer that item. In the time the item from secondary input is transfered, transition buffer on the priority input fills up and the splitter goes into expected mode of operation. You may notice that items on the input priority belt are never stopped (if you would have a priority output connected here from an earlier splitter, there would be no items discarded). This splitter outputs items slightly too early compared to non input-priority one and that is required for the priority mode to work correctly in all cases of item offsets.