mudbox shows the objects smooth without smoothing groups...
if you need smoothing groups you have to use the new 2012 SAP version...
older versions of mud have no smoothing group support... but everything will work like it should...
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edit:
now i see it...
you mean the triangulation..?
have you installed the latest fbx version..?
http://usa.autodesk.com/adsk/servlet/pc/item?id=10775855&siteID=123112
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