Illustrator :: Seamless Repeat / Clipping Mask - No Stroke Width

I am trying to create seamless pattern repeats. Most of the time when I do this I get thin lines between the tiles (I place the original pattern and move>copy it to exact measurements). I have read in other forums that these are 'ghost' lines which don't appear when the design is printed out, but I've had fabric samples printed that do contain a line. Also sometimes the motifs on the edge of each tile don't match up - see the slight line down the orange / white cups here:
 
I move>copy the motifs using the exact measurements of the artboard, I line up my clipping mask with the artboard and they are exactly the same size, and they have no stroke width. I can't work out why it still does not work.
 
Even before I copy and tile the design I sometimes have a thin white line down one side - see below.