In my case, windows was not remembering it, what happened was it never enabled (or started using) wired connection, even though it was enabled. I think windows uses wired connection as priority, but for some reason it wasn't routing data via wired through dock.
Access Connections is a bit flaky, it hangs when you want to modify settings and save them, but once saved, it runs seamlessly.
8/18/2011 - X220, Intel i5-2540M, 12.5" IPS, FingerPrint, Cam, BT, Intel 6205 Wifi, 8GB, U2312HM on Mini Dock Plus 3
1/15/2012 - S405 (Wife's), AMD A6-4455M, 14", 4GB RAM, Windows 8
7/02/2015 - T450s Intel i5-5300U, 14" FHD IPS, FingerPrint, Cam, BT, SSD, Intel 7265, 4GB