Oh yes, there's a weird design issue, but it's not the filter. The fab can call through the filter, as long as it's set to the correct kind of resource.

The problem in this case is that if you have raw resources going in a circle around two refineries, and they are all spaced out a certain way, then the fabricator seems to send a refine call to one, then the other, alternately.

But the resources end up being just too far away from each to jump in the hopper at the right time. So the fab calls the other refinery, meaning the first one stops "pulling" and the raw resource skips past it instead. When it gets into this state, the raw resources will endlessly circle and never jump into either refinery.

The only solution is to either pull one refinery off the conveyor, or pull a conveyor track off so the resources can't skip the refineries, but are forced to go through them.

Neither solution is optimal for general production though.

Have you been having crafting problems? You have a filter there set to feed a fabricator refined wood? I didn't think a fabricator could call for resources through a filter... That it would block normal function (just wants to be connected direct to the conveyor line)...