When I clicked on one of my appartment blocks in town, Good Meals where at 3.8 out of a capacity of 6. (Good Meals were required to upgrade the building at this time.) Hovering the mouse over “Good Meals” I was told that 4 unit where on its way (with 2 units per car due to medium difficulty). Indeed, a bit later two green cars drove into the building, with a distance of about one second. The first car filled the Good Meal bar up to about 5.8, the second car just vanished and did nothing (not even filling up the bar completely). That means a loss of 50% of the resources involved, and I could observe several more such instances happening at other buildings in the next few minutes, so this bug seems to occur regulary.
Then I built 6 steel factories and 3 engine factories (including supporting industries) and connected them with a single collector/distributor pair (over a distance of just 20 tiles). I set both collector and distributor to a capacity of 1000 for steel and waited. When the distributor was full, strange things started to happen. When the engine factories required resources, about a dozen steel units where faithfully delivered, but then the collector sent out more than a hundred units of steel. The moment the distributor was at full capacity again (i.e. enough cars had arrived to fill it up to 1000 units again), the collector stopped emitting cars. Of course, the resources still on the road just vanished when the cars reached the distributor, as it could take in any more. That means a loss of almost 90% of the recources.
In my opinion, some buildings do not check their own max capacity when requesting resources, especially living quarters and distributor centers.