Just checking back in to make sure that the problem has been solved. Has anyone had trouble with pets which were removed from the trade reappearing after the trade has been sent? (in the last week, that is, after the fix was applied). If so, which internet browser are you using, and (important) which version is it? (go to Help->About to check the version).
EDIT: Looks like the "Remove" button was absolutely broken in Internet Explorer 6. You would have seen the display get a little corrupted (pets jump to odd positions or get squashed together), and the pets would still have been greyed out in the "Browser for pets" dialog, since they were actually still part of the trade. I've made a fix that seems to cure this issue. You should still consider upgrading to a proper web browser like Internet Explorer 7 or (even better) Firefox, http://www.getfirefox.com