What were you doing? I do this sometimes when doing Leves and stuff because of a lack of mobs or something, I notice 3 other people trying to kill the same thing so I will shoot blind invites. Usually they accept and we kill everything we need then drop party. I will usually accept blind invites also in case somebody was trying to do /tell and clicked the wrong thing, usually to ask for a raise or something. Never has bothered me, if its totally random after I join I will just drop the party. its just 2 clicks of my time.