Hi
Indeed it isn't suppose to make any difference to sync speed or margins.
Either vectoring has also been enabled, or updating the firmware in the cab and enabling G.INP has knocked a couple of people of line until they reboot or update their own firmware. If those few people are the ones causing the majority of your cross talk, you could be seeing perhaps only a temporary improvement.
I suppose the other possibility is less errors for everyone allows other modems to back down their power outputs, so reducing cross talk?
Be interesting to see if it is a lasting effect.
Regards
Phil