Intermittent mixing of belts with different speeds

[amirlb]

While manually upgrading the main bus, I came across a situation where one belt spills into another. The spill is rare and happens once per several hundred items.

The schematics are as follows:
Belt 1 and 2 are parallel and adjacent and contain different kinds of items. Belt 1 is yellow (slow) and belt 2 is red (fast). Both are almost full but not compressed.
At one tile, belt 1 enters underground (yellow underground), and on the next tile belt 2 widens into a splitter (red/fast splitter). The splitter occupies the space belt 1 would have used if it didn't go underground.
Both arms of the splitter get some items from belt 1 in this case, but very rarely.

The version I'm playing is 0.17.74.

[Loewchen]

What exactly are you considering the bug? That items can enter an underground belt from the side?

[valneq]

What Loewchen describes is a feature of underground belts detailed here:
https://wiki.factorio.com/Belt_transpor ... belt_lanes

At one tile, belt 1 enters underground […]
Both arms of the splitter get some items from belt 1 in this case, but very rarely.

But it sounds like the items spill out of the underground in this case. Can you post a screenshot?

[amirlb]

I revisited my previous saves on the same map, before and after the stray items appeared on the incorrect belt, and tried to reproduce both there and in a cheat map. Couldn't recreate it, so please consider this a false alarm.

There's no bug as far as I can tell.

Is there a proper way to close this report?