The short answer is "it's never actually been used, so plainly no one really is comfortable with it"
The longer answer #1 is "According to xorxes' opinion, as a member of the BPFK, and expressed on the proposed definition page
http://www.lojban.org/tiki/BPFK+Section:+Irrealis+Attitudinals, it should be used as an offer: .e'o nai ko lebna lo titla
Here, have some candy."
The longer answer #2 is I believe that "negative request" means an _expression_ of desire that something not happen: ".e'onai do citka sepi'o lo degji" "I really wish you wouldn't eat with your fingers"
--gejyspa