I used these flashes with no trouble on the XTi and 40D, but they are having a terrible time communicating with my 50D. They won't recognize the focal length (just go back and forth), and my recycle time has gone from a couple seconds to at least 15-20 seconds (I've tried multiple batteries in both camera and flashes). Has anyone else noticed this? Canon wouldn't help since it's not their flash, and I haven't had any luck reaching Sigma yet. I really don't want to give up on these flashes since they slave, but they're not usable like this.