It no longer causes it to hang, but it does give the following error - "An item with the same key has already been added." - and all the 3dshapes revert back to their default settings losing all of the edits that were made.
The steps taken were:
Open 3DNes.
Load the rom.
Click on the item to edit. In this case, I chose a rolling barrel that had SizeZ set to a different value than the rest of the frames. It is set to 12 while the rest are 10.
I adjusted the SizeZ value from 12 to 10.
Saved the 3dn.
Exit 3DNes.
Reopen 3DNes.
Load the rom.
That's when the error occurs.