Common Sense: Working memory imbalances don't interfere with working memory in every circumstance, they only gum up the works, like molasses in January.
One of the main reasons some of the stimulant meds don't work effectively is that they don't cover every essential neurotransmitter system necessary for efficient pre-frontal cortical communication.
Prozac and Paxil significantly block the metabolism, the breakdown, the effective use of amphetamine products. The results: crazy but quite predictable drug interactions.