Got the house painted professionally a year + ago and in the last few months have noticed brown patches appearing through the cream gloss paint on our doors upstairs and downstairs. They were perfect when painted. Anyone any idea what this is and do I need to chase the original painter to fix it. He used paint that he mixed himself adding a brown oil from a bottle to the tub of white paint - maybe this isn't the best thing to do? Or is it something to do with the doors - they're not great quality. Thanks.