I know this is an old thread but I had this issue could not go down a slope without painful cramps in ball of feet and had to stop ever minute or so .. Green slopes were unbarable etc nightmare... Pain was bad with both Flows and Burton P1 bindings, Previous boots i had were Burton and some other makes (cant remember) all gave me pain.
My solution was a pair of Quenchu Snowboard boots... I dont know what model they were but they were very cheap about £20 at the time... and the only thing I can think why the pain stopped was because they are wide and even if i try and tighten the straps on bindings down on these boots compared to other boots I have had they seem like they can cope with the pressure of the straps (a bit like steel toe capped boots for snowboarders lol ).. When i get home i will try and find out the model of boots I have...and post...
But good luck as until i found these boots i wrecked 2 holidays.... :