The trim is in corners...condensation stays there because of poor air movement in the corners - less air movement - better chance of mildew.
Also - you may have alkyd paint on your trim - and latex on your walls - the alkyd binder is food for mildew - and is more likely to do so than a latex.
So - clean with bleach and water - prime with Glidden Ultra-Hide Gripper - finish with Glidden Evermore or Ultra-Hide Latex semi-gloss - and install a fan to remove moisture or move the air around...