Recently picked up some new 600 ex rt's and a ste3rt. Fabulous system. But for some reason I've noticed on occasion that when shooting in AI SERVO (and back button focus), I'm getting an occasional red lit AF confirmation. Seems to be more common with the flash set up but I recall very infrequently it happening prior. Body is a 5d3.
Doesn't seem to be a big issue but wondering if anyone else has noticed same?