If you shift the left margin marker to the right a few inches on the ruler in a ClarisWorks word processing document and turn off Show Margins, you will notice a shift of the left margin marker about a millimeter to the right.
If you print the document, you'll find that text prints about a millimeter to the right of the margin setting. This happens whether "Show Margin" is on or off.
The problem seems to be that the margin settings are not accurate when the margins are showing.