I've stumbled upon "_bindtype" system variable, which kind of surprised me. I just can't find any use for it and it works differently than I would think it should. 

The only thing it seems to change is the default option while binding a whole Xref file to another drawing:

_xr -> rightclick .dwg xref file -> bind -> "Bind" or "Insert" options.

On the other hand when you try to bind separate parts of an Xref it doesn't seem to do anything:

_xbind -> choose .dwg file -> choose Layers or a block for example -> "Add" -> OK.

Even with _bindtype = 1, which is a "Merge" option it actually doesn't merge the layers. All the layers which had been bound this way or objects drawn on some layers and bound to new drawing keep their separated names and $X$ numbering.

Do you know of any other way this variable comes into play? Also, is there any other way of binding parts of an xref into a drawing and merging layers besides going through them manualy and merging them in Layers Palette or manualy changing their names in order to break their connections to the source drawing?

Side question:

What I also noticed while using Design Cented (_dc) this time is that when I insert an object using it the layers palette doesn't update newly imported layers untill I save the file. "Refresh" button in the palette doesn't update it either. It would be great to be able to see/use layers without saving a drawing just in case. Any solution to this problem? (_regen doesn't work either btw.)