For those interested: I found out that the connection is reset when the DR goes into idle mode. More specifically: when sysd calls idle.sh.
To circumvent this you can disable idle mode when using usbnet:
gconftool-2 -s /apps/er/sys/power/idle_mode FALSE -t bool
Using this instead of the "mount -o bind" over /sys/devices will give it more normal functionality while using usbnet. This setting is reset after a restart though, so doing an xserver restart will kill the connection.