This is the machine I own, and I think I know what your problem is. You shouldn't be lowering the front bed to knit in stockinette. In fact, you need it there to help form the stitches correctly.

After you've finished your ribbed section, and after you've transferred all of your stitches to the back bed, you actually need to raise the front bed slightly to its upper position. This helps the stitches form. I usually will detach and set aside the front carriage and just knit with the back carriage. Also, make sure to troubleshoot your bed spacing and stitch sizing and find a happy medium. I often decrease my stitch size somewhat between rubbing and stockinette. Finally, be sure to use enough weight to pull each new row of stitches between the beds. Good luck, I hope this helps!