so why did Dancesafe say they got a "slow change to black"?
my theory is that the pill they tested had once been stored in a baggie with other pills, some of which were MDxx. this put enough MDxx dust on the pill to give a "false positive" to the reagent test, but probably not enough to significantly register on the lab test.
or perhaps the knife wasnt properly cleaned that scraped the pill, or the surface it was tested on wasn't washed properly...
Dancesafe uses (relatively) untrained volunteers, who work in loud, crowded, distracting environments. I'm not hassling any of them for maybe screwing up a test or two, because I do the same work they do and understand how hard it is. and anyways, the testers were sufficiently worried about the reaction to forward the pill onto the lab for full testing.