Part of the problem was probably that it was a stiff boot.
I do have some things i have to do when putting on my Burtons in order to keep it from pinching the back of my leg. Nothing entirely special though, just make sure my socks are pulled all the way up, my UA leggings arent jammed down in there and are pulled up over the boot...
'09 151 Never Summer SL-R
'10 K2 T1 DB Bots
'09 Burton Cartel Bindings