I signed up today just to help you. Bask in my benevolence.
So far in these threads I've seen people mention that you need to preserve the number of vertices in the model, but this isn't the only step that needs to be taken. You also need to preserve the vertex order and the number of faces. For example, when importing a wavefront obj into blender, by default it will re-order the vertices. So, you will need to revisit the import options and make sure that the preserve vertex order box is checked, doing the same for export. 3DSMAX does this automatically. In blender, I've noticed that on a handful of overworld models it sometimes erases a random face from the object when importing, and this will also cause a graphical glitch in-game. But since we are preserving the vertex order, we can simply copy and paste the list of faces from the original OBJ into the new one using something as simple as notepad, which will resolve any issues when importing your edited object.
I hope this is helpful to you. I'll be happy to give you more help should you need it.
