With regards to ubuntu, I see your point. 

With regards to the bugs on dev versions, I was using the latest official release (0.10.1) of Tilemill when I encountered the layering bug - https://github.com/mapbox/carto/issues/283 which was fixed since then then. 

I don't want any potential contributor to the project to have to experience the aggravation that I had and until a new official version is released, I think it's worth mentioning the use of master.