If you turn off Sprint toggle in the options....it works fine unless you hit ESC and then get out of it (ESC again), then the sprint is back to Toggle (ON) state.
I'm not able to reproduce this behavior, are you positive you are hitting 'Apply' after changing the setting, and before pressing 'Esc' to back out of the options menu?
If you have another keyboard, switch it out and see if it still does it, had that happen to me on a different game, turned out the spring in the button was getting worn out.
