When sprinting (double tap [W] by default) up or down a hill I think it would be intuitive for the character to maintain the fastest possible speed. To move as fast as possible in uneven terrain at this moment it is necessary to switch back to normal walking to go faster. Especially with the fastest sprint being in 'fighting stance' it requires a lot of switching back and forth between normal walking and running (and between fighting stance and normal stance) to do just one thing: go as fast as possible.