Hi,
that happened today in my game against Buffalo.
http://mfn20.myfootballnow.com/watch/122#24023
A fumble never recovered by anyone. And if you look at the Fumble stats on that page :
http://mfn20.myfootballnow.com/box/122
My players fumbled twice and recovered their own (both for safeties btw ^^) but one of my players (Bolden) forced two fumbles on Green that were never recovered (ideally if you had all the fumbles in the game and all the fumbles recovered, the numbers should match... Except if the ball is going out of bounds after the fumble I guess)