I made some sort of furniture by taking the default cube and insetting some parts of it and splitting(subdividing) it here and there. Then I add a bevel modifier with 1 segment.

A view of the model, with modifier applied (as you can see there are only quads here):
[![model view][1]][1]

Here is the blend file:
http://michaelroeleveld.nl/src/downloads/abstractFurniture.blend

I export it as obj, the only box I have checked is "apply modifiers".
In the exported obj you will find a couple of faces which have 6 vertices, which shouldn't happen. Why does it and how do I fix it? It's important that this mesh gets exported as an obj with only quads/bilinear patches


  [1]: https://i.sstatic.net/vqDCm.png