Bad surface finish on one side of model, unexpected fix

[Gian Pablo]

So I recently posted this http://www.thingiverse.com/thing:417803, based on http://www.thingiverse.com/thing:398548. The walls in the original model are 1.2mm thick, so I used that as a default in my custom version.

The print preview showed 3 layer traces side-by-side, as expected. The layer width in Makerware is 0.4mm. However, when printed, the surface finish is really bad on 3 sides. Curiously, the internal partitions are not affected at all. Multiple prints of the same object showed exactly the same defects in surface finish - the ripples were in exactly the same place.

I had read some previous threads about similar problems, mostly pointing towards issues with drafts and cooling. However, I suspect the issue is really a bug in Makerware. I modified the model to use a 1.6mm wall thickness, and it printed perfectly. (See picture)

Here are the two versions side-by-side, same printer, consecutive prints, the main difference is that the model on the left is using 1.2mm wall thickness and the one on the right 1.6mm:

So for anyone experiencing issues like this, check your wall thickness and number of shells. Something might be up there.