Speedlite 580 EX II Master / Slave HELP
Weird. I don't have the EX II, but I've got the 580 and 550 and some of the earlier Canon speedlights and I've never had this issue. I use them all the time for location biz portraits.
Try this. Try setting them on 1/8 manual exposure and see if they sync properly. Also, maybe there is an issue with second curtain sync. (I'm thinking some sort of tricky advanced setting has gotten dialed in. Canon has some doozies.)
Finally, if worse comes to worse, these days I use a set of cheap radio slaves to trigger my stuff.