With the Revit Issue and the ID Element numbers; I've just discovered the following. Can someone just confirm it; I want to ensure I'm not going mad. (I've tested this on Navisworks Manage 2012 and 2013 – all service packs included).
It looks like the Clash Detective is working off the "Last Object" resolution. The Typical Revit ID number is working off the "First Object" Resolution.
However when an object changes in Revit (Change the type of a piece of furniture, or change the wall thickness and thus a door frame thickens) the "Last Object" Element ID changes number.
Thus if you had previously run a clash and found a clash between e.g. a door and a beam (a clash was found),
And then the following week, the wall hosting the door changes size (thus the frame changes) on export to NWC the "Last Object" Element ID has changed.