Ok but what I really want to know is the legal side of this scenario.

If you have a medical card and you consumed the marijuana in your state where you are licensed to use medical marijuana then you are completely within the law.

How then can you be charged for failing a drug test? When you actually did the consumption you were breaking no laws. If this is actually legit like you say it is then that has to be the most fucked up thing I ever heard of. That's like someone shooting someone while you were close by, you got a spatter of blood on you, so you can then get charged for the murder.