Well to use a previous poster's example, arsenic wouldn't flush. It's a relatively immobile biologically. Once it is taken into a plant or animal, it will stay there without the use of some sort of chelating agent. Now, think about mobile atoms and molecules like nitrogen, phosphorus, calcium, etc. If you're using a hydroponic system where you are in complete control of nutrients, then when you cut off nutrients, what happens to the mobile stuff? Well, at that point, the plant will begin to starve, and what happens to a living organism when it begins to starve? In people, the response is to horde nutrients and reduce metabolism, among other things. It only makes sense that by starving a plant, you will probably have a poorer outcome than if you had continued feeding.
Again, I've never run an experiment with flushed and unflushed to see if that's the case, so don't take what I say as gospel. But these responses are pretty standard among all living things, so it would be a shock if it weren't the case with this marijuana.
