I had a look and, auto-removal happens when you actually press the 'Sync from Steam' button on Wishlist or Library tabs. Either way it'll delete wishlisted items that are found in your library, and offer you to re-add them immediately.
If the auto-sync was done without your input, then it'll wait for you to go to the Wishlist tab and ask for feedback, because if you go there (e.g. through adding multiple games to the same time to your wishlist from a bundle), you're slightly less likely to notice the messages posted over there than if you actually asked for a sync. So I'm not doing it for you, yes. Well, I do, once you confirm it's what you wanted.

All I wanna say is, Barter isn't as transparent or practical about wishlist handling, so... Maybe you should consider LT's way the 'proper' way to answer to the needs of every kind of trader..? I mean you *can* simply press the button and as soon as you see your browser sent the data (e.g. says 'loading' or stuff like that), you can do whatever else you want, the data is saved. It's really not a biggie...