Open the sheetset manager database and you will see that if the data base is accessed by multiple locations, the UNC path is changed to the local server regardless of the mapped drive path.
It does the same thing for anyfile kept on a local server, in fact, it changes the paths because it keeps copys of the xrefs on your local computer anyways, unless you tell it to do something differently....
AutoDESK hasn't changed how the paths work since the inception of arg files. The program is not designed to play nice with a complex network and the more you dig into the more obvious it becomes. You really need a Network or Software Engineer to customize your WAN, LAN, hardware and software in such a way that it replicates the program functioning with files retained "locally" i.e. on your c drive, like autodesk initially intended it.
John Hammer, LA Dell Precision T3500 - Xenon W3550 @ 3.07 (4 core) Ram @ 12Gb 64bit Win7 Pro Samsung SSD NVIDIA Quadro 2000 - Dual Monitors Cat 6 network with GlobalScape Avail Agent - WAFS Infrastructure Design Suite Premium and Civil 3D 2012