The dumping controls/restrictions seem to apply not to where the material is being dumped but where it is being dumped from. If you have two different mine control areas with different settings, a truck can dump a material designated for one area into the other area along the border. See image - I'm trying to build out a rock border using the lower (non-highlighted) mine control zone which is set to only allow rock. The global settings are to allow dirt only - and the truck shown stopped in the global area (which was already completed - at full height) and dumped dirt into the adjacent zone. My assumption is this is because it was allowed to dump dirt in the tile it was on, even though the destination was the adjacent tile which allows only rock.
I've seen the same behavior happen with two adjacent mine control areas (not necessarily using the global setting) as well.
