Previously "approved" clashes showing as "new" and "resolved" when dwfx models updated

Hi,

We are using Dwfx files because NWC files export out of of Revit with fragments of other levels in them. Autodesk suggested using Dwfx as a fix when our service provider KarelCAD upgraded the problem to them.

Anyway the problem is that when we update the new Dwfx files in Navisworks each week the previously "approved" clashes dont show as appoved anymore but show twice as "new" and "resolved".

We have checked the element Ids and they are the same in each case.

Any ideas?