[totaltec]

So! Here we go:
The nth child of the list is being cleared. Consider this CSS:

@media (min-width: 1200px) {
  .no-sidebars ul.products-grid.grid-list li.product-cell:nth-child(4n) + li.product-cell {
    clear: none;
  }
  .no-sidebars ul.products-grid.grid-list li.product-cell {
    width: 20%;
  }
}

See the ".no-sidebars" in the class definition? That is crucial to work on single column layouts.

-Mike