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Here is a pic. Not sure how well you can see it from here. As expected, it seems to get worse when the weather is warm and humid. These mouldings are tacked in with nails in the first place so I'm thinking it's not a problem. Guess I should call customer service to get a ruling on nail length.
Based on your description, it sounds like Jeff has it right. It's cut a bit too long and expands with humidity. If you pull it away from the wall towards the end of it, you may be able to see how much excess needs to be trimmed. If there's wood behind the wall board, you could probably use a 1 or 1 1/4" brad on it. If you shoot into the styrofoam behind the thin wall board, it won't hold for long, therefore the recommendation for the adhesive.
I had a piece of trim along the closet at the entry door cut too long, so they fired a pile of brads into it and then snapped it to lay flat (which it didn't). They covered the half-axxed job with the fire extinguisher. I fixed it.