sounds like it could be related to either a tight calf muscle or a large calf muscle, the fact tht your tele boots bend at the ball of the foot will reduce the problems in this type of boot......
if the calf is tight as you flex forward you will load the ball of the foot and put strain on the calf which does not have the available range of motion to make the movement you are trying to make...the B 90 is prtetty soft so you could be over flexing it..as above the tele boot will bend at the ball of the foot therefore you do not need as much ROM
if the calf is big it may just be pushing you further forward than you need to be, this in itself is enough to give major calf cramps and thigh burn
tight calf...lots of stretching, a heel lift in the boot, possibly bolt the cuff to stiffen it
big calf ....heel lift to lift the calf up and out the boot a little, then have the cuff of the boot bent/flared back to allow a sligthly more upright stance [well at least stop the calf from binding on the back of the boot]