oxycodone is an opiate. morphine is also an opiate. drug tests often cannot distinguish between the type of opiate that is detected so as long as you are taking prescribed medication there is not cause for concern. drug screenings are very odd. i bought home tests to screen my boys for drugs. it came pack positive for both of them for pcp. that was so terribly wrong that they laughed and confessed it was only marijuana. i was relieved but still not happy. i don't know how you would validate any test being better than another but i don't trust them.
i too am on oxycodone and clonazepam pain management had a urine test positive for morphine which i've never taken.