I realize that this is an old topic, but I just ran into this problem after using a new lot that I found in the gallery. I'm posting the fix that I found based off reading this thread along with trial and error. My lot has 2 ponds. I discovered that my sims were not only running through a pond every time they left the lot, they were also leaving from the back door, running behind the house, then running all the way around the lot to the front before leaving. I set up a fence around the entire lot, which caused them to use the front door, as well as to stop running through the ponds. Once they didn't have to run through the ponds, they stopped changing into a swimsuit. Hope this helps anyone else having this type of issue!
