ZBrushCentral

OBJ Export Import resizing issues

I am having an issue with obj files resizing when exporting and importing.

My workflow consists of starting in Maya or Rhino with a base mesh and importing it into Zbrush.
I usually duplicate a subtool before importing.

This workflow usually works but occasionally,
If I go back to Maya or Rhino and back to zbrush again the OBJ Will move in location and scale up.

I have also noticed depending on what subtool I am on that it will effect the import size.

Any thoughts???