actually theres a message alert that an Xref object has been move to unsupported location (0,0,0) if ever you accidentally do it.
and also once you closed and open the drawing with moved xref, theres is a message again in the command prompt that tells
XREF xxxxx.dwg is attached at a non-supported location. Connections can only be made to models attached at 0,0,0.
even when you reload the xrefs, this message appears.
well i hope they can do it into a pop up alert message dialog rather than appearing from the command prompt.