Does anyone know what the bugfix in 0.8 that is referenced in the title of this thread does exactly? I'm afraid it has consequences for my lane balancing, and I would like to know exactly what it does before I update.

since 2.0.56, it is possible to explicitly state whether an inserter should pick up from the left lane, the right lane or both (see https://lua-api.factorio.com/2.0.56/classes/LuaEntity.html#pickup_from_left_lane). Before the 0.8 release, an inserter would prefer one lane (left or right) but if no items were available, it would start picking up from the other.

If you have a belt that has one item type on the left lane and another on the right and funnel that through a miniloader, it would be possible that items from the left lane end up in the right and vice versa. With the 0.8 release (and beyond) this no longer happens. Each inserter is locked into either the left or right lane and there is an equal number of inserters for each lane. This makes miniloader speed computation much simpler.

Does that answer your question?

Does that answer your question?

It does in part! I am assuming that items from the left lane are now unable to ever cross to the right lane? I sometimes use the loaders as a compact lane balancer, I'm guessing that no longer works then?

EDIT: For clarification, what I currently use it for is making sure that a belt that is fed on only one side (e.g. the right) has its contents spread over two sides such that it ultimately buffers over the entire belt (I recognize that this isn't an actual throughput increase).

The miniloaders will not balance the belt or distribute items from one lane across both. The fact that they did in the past was a) an unavoidable annoyance based on how the miniloaders were implemented and b) never balanced because the internal inserter pairs are not coordinated.