Two borders make a happy cell

HTML tables can be confusing and frustrating especially when using Dreamweaver, the auto widths can mess the table up.
i noticed today that when i wanted to make a table (11x8 cells) with a outer border, the cells that had

eg:"style border-right: 1px solid #666;"

had widths Dreamweaver recognised as incorrect un-till i added a border on the other side.

eg: "style border-right:1px solid#666; border-left: 1px solid #fff;"

i still haven't figured out why yet but i think it has something to do with the extra pixels being added to the widths because of the border.