Some airfoils with round leading edges stall abruptly, some sustain lift for several degrees increase in angle of attack while the drag increases a lot before loosing lift and some airfoils with rounded leading edges don't recover lift after a deep stall untill the angle of attack is reduced well below the stall angle of attack (hysterisis).

Any airfoil which has had the leading edge only modified from round to sharp will stall at a lower angle of attack than its prototype.