One of four box walls not solid

On two different models I have a basic box with walls that are 1.2 mm (3 nozzle width) thick. When I slice using MatterControl and print, three of the walls are solid with three perimeters but a fourth wall only has the inside and outside perimeter with a gap in the middle. This does not occur with Simplify3D sliced models with the proper settings. Does anyone know which setting(s) I need to adjust in MatterControl to solve this problem? Would prefer to slice in MatterControl to take advantage of the auto bed leveling on the Pulse.

Mystery solved. Because the only fractions that can be precisely defined in binary are fractions with powers of 2 in the denominator, it turns out that floor(1.2/ 0.4)=2 and not the expected three. The MatterControl slicer must not allow for the imprecision and it assumes there are only two 0.4 perimeters and since there is no single extrusion gap fill (ala Simplify 3D) that I have found, it prints the two perimeters and leaves the gap. I have found that if a change the wall to be 1.21, the slicer sees three perimeters except when there are fillets on the corners. Using 1.22, the slicer also sees three perimeters for the corners.
This is not an elegant solution. One that might work universally is to set the nozzle to 0.39999999 in the slicer but I have not tried that.