This effect is not caused by the paper being moved within the printer. It is a result of the Color Photograde technology creating colors from patterns of dots. The pattern is more noticeable with lighter colors next to solid black. This effect will also happen when using solid cyan or solid magenta. Most users use colors that are a combination of these pigments, such as blue, which is made of 100% Cyan and 100% Magenta so this effect is not usually noticeable.
To prevent the white line from appearing, you can create black out of Magenta, Yellow, and Cyan in 100% shades. However, this increases the cost per page and produces a more charcoal colored black.
If the line appears to be more than 1/16th of an inch, try using a different paper type and selecting Best from the Options menu in the Print dialogue box.
Note: Other laser printers and solid wax printers will display this effect, but sublimation printers will not because they actually create continuous tone images by varying the heat applied to solid pigment.