After a little more digging, I think I have your answer (and mine too).
Google for "Surfactant Leaching"

Although the picture on all of the pages is rather extreme, the
description and conditions match our scenarios almost exactly. A rare
condition, and apparently almost always with newly applied paint, and
relating to humidty and moisture.

You obviously had moisture problems. My closet gets very humid, because
it is unheated and in a far part of the house.
-Kevin