Careful about making assumptions...broken leg is a result of impact...ABS is not a cureall for collision avoidance or steering supplement to plain ordinary experience and riding skill.
What was the circumstances by the time 20mph happened, did you grab the brakes and recall feeling the pulsations of ABS working, until the collision, or did it just happen so fast, ABS did not actually come into play?
Lot of circumstances, conditions and tactics before during and after the accident that need to be answered before conclusion that ABS was truly the root cause of the accident.
For example, how much speed had been scrubbed off before the 20mph lockup incident occurred being one. Did you let up so the ABS suddenly stopped and high sided you?