You are missing nothing, Not possiible I'm afraid (Filters are saved only as in options >filters only) Each time you turn off Limewire the search history and browse history is cleared.
Try copying / typing ip nos or search terms into notepad or text edit and using them again from there, but note that many ip numbers are variable and each time some hosts switch on they have a different ip number.
Many times this has been requested in feature requests...
