I received my new O2 foot last week. I haven't used it yet. I also had problems with the 1/4" foot that came with the Horizon. I took the 1/4" foot off my Elna, placed it on the Horizon, and no more problems going over thicker seams. It just has something to do with the design of the original foot. The guide on the original foot is too loose, and that may cause the problems. Have no fear! Just keep using the machine, it only gets better with time. Mine has!