external references in assembly

Hi -

I'm working on a part, that is being used in an assembly.  The part has a cavity that I've created using the "insert part" command and the subtracting that body from the part to create the cavity.  This part is then being put into an assembly.  However, when I go to edit the part within the assembly, i get a message of:

"this part has features defined in teh context of another assembly <XXXXX file name>.  You can edit the part, but not create any external references to the components of the current assembly"

I'm running 2013, and I don't remember having issues like this using in 2012.  why is SW treating an imported body into a part as an assembly?  Is there a new switch someplace in the settings that I've missed?  Any help is greatly appreciated.

thanks

Joe