From the winlav.dev.java.net project: The drawing mechanism for disabled text in a JButton under Windows XP draws the text 1 pixel to the left and 1 pixel up from where it should be
https://winlaf.dev.java.net/release_0.5.html#Issue47

In recent builds of Mustang it appears to be off one pixel vertically but no longer off horizontally at all. Confirmation needed.