Hi, I run my drawings on AutoCAD 2016 and I came up with this problem. Out of nowhere, part of my XREF are copied in my drawings as if I typed _NCOPY (express tool command) and selected objects in the XREF but I didn't. I checked my command log and I can't find anything related to that. My XREF is the building floor structure drawing and it's inserted as an XREF in the architectural drawing. Both of them are opened in AutoCAD at the same time. I'm actually fixing the building floor structure drawings of every floor of my building and in every architectural drawings in which these Xref are inserted into I got these unwanted nested object. Can anyone help me?

Any way you can turn back time and open a drawing that does not have the nested object?  Do you have a backup copy of the drawing before the big OOPS?

No, I can't go back in time with my drawings but I do have some drawings which do not have nested objects. I can delete these objects by myself because I know which one aren't supposed to be there, that isn't a big problem. I want to know what did that , if there's a system variable I need to change or if it's simply a bug. Another thing is these objects have no layers when I click on them. I tested another drawings and tried the _NCOPY command to see if the objects where on a layer and they did...

I doubt the problem has anything to do with a system variable.  Most likely you hit some odd combination of keys without realizing it which then wreaked havoc upon your drawings.