LHOOQ...did you make the 7750 into a manual wind? If so, I'm assuming that you also used the lower profile case back that DW sent. I think this is the cause of the problem. If you look at the lip of the lower profile case back, you will notice that it is thicker than the 7750 case back that fits the auto wind mechanism. The thicker lip prevents the chrono from resetting.
I had the same problem as you did, but when I fit the thicker case back onto the my Daytona, everything worked as it should. You will also notice that with the lower profile case back that the 12 hour sub dial will drift. This will also go away by installing the thicker case back.
Without having to take the case back to a machinist, I'm currently trying to figure out how to thin the lip of the low-pro case back, so that all the chronograph functions work perfectly with the low-pro case back.