There was a similar case locally recently. A neighbor had called about smelling marijuana and the leos went to investigate. The door was ajar and the officers walked in and found the son smoking weed in his room with a window open. They looked around in plain sight and found scales and bags of weed for sale. He is in jail right now on the charge. I think it would depend on good faith and the judge's opinions in your county. If you are acting in good faith and under the scope of authority of your job I don't think you would get jammed up on that at all. I think it would stick as a valid charge. This arrest was after the suspect opened the door and let them in voluntarily so this would not be the same as MSU is describing. Just my opinion.