When you say ten percent are you referring to the percentage of people who get tested and get results from other drugs they have taken or ten percent that have taken a drug that metabolizes as methadone?
there are many that get false positives and the UA shows they are not taking there medications and I would say that percentage is very high, certainly higher than ten percent. I have a study done by the Va that shows as many as 44% tested negative for opiates when they were taking them.
This can be found here...
http://www.medhelp.org/user_journals/show/97621/False-negative-urine-test?personal_page_id=863283.
I am sorry you are in the position your in. We have to be very careful about honoring our contracts. With everything going on right now and all the negativity involving pain management we really have to stay on our toes and follow it to the letter.
Did the Doctor drop you because of the UA showing drugs you were not prescribed?
if not your very lucky as they usually do.
Live and learn, this is something that you can not change but most certainly have learned from. In the future you should see your PCP if you need other medications and follow your PMP contract for receiving other narcotics.
you can try and talk to your Doctor and explain you made a mistake and you will be more diligent in the future.
I hope it works out well for you:)