That's what is different! You plotted to dwfx and I exported to dwfx.
Using the DWFx ePlot.pc3 printer config provides a dwfx that Design Review is able to display the image file.
Only problem with Inventor is there appears to be no equvalant to the printer config file that Acad uses to create dwfx files.
Thanks for your help Dean, it got me on the right path anyway.
Just noticed today that the image files used by Inventor to display threads are visible in dwfx files.
Instead of modeling real 3D threads which would take up alot of system resources to display and/or calculate their geometry, Inventor applies an image which looks like threads.
So apparently flat images won't work but images applied to curved surfaces do?!?!?
Something doesn't jive here!