I've tried a variety of flat strings on my EHB now. Couple of sets from D'Addario and La Bella and one from Ernie Ball. I'm getting quite a few dead strings of varying degrees, something I've rarely experienced with traditional tuners.
It looks to me that there's tendency for the string core to slip in the string clamp at the head if the allen bolt is not tensioned correctly. Bending the string end over doesn't seem to make much difference. Perhaps it's down to how well the string is clamped which is worse with flats. I've only fitted one set of round wound and they were fine