Comment 25 for bug 160413

http://www.linuxquestions.org/questions/linux-networking-3/realtek-813981688169-on-2.6.21.3-or-newer-593495/

speaks of a setting in Windows XP which prevents same from leaving the NIC in a state from which the linux drivers cannot recover.

That all said I am suspicious of network-manager given the reports that this problem only emerges when the full gui is booted.