This problem has been bugging me for ages and I can\'t seem to fix it or fully localize the source of the problem (although at times I can force it by allowing the phone to Stan
I had a similar disconnect issue in which the connection gets lost soon after a reboot. On my LG VS840 4G phone, changing the USB connection mode from Mass Storage to Internet Connection helped. Apps Key > Settings > Connectivity > Default connection mode > Internet Connection.