Table rows not lining up on right edge

I could really use some pointers on this. I'm crafting a large document that has many tables. The tables have a black, 100% fill on the first two rows, then an alternating fill of 25% black for the rest of the rows. On some of my tables, and always on a table that is near the right-hand edge of the page, the first row is slightly longer than the rows that follow it. This isn't every table, just specific ones. They weren't crafted differently than the other tables, so i'm at a loss.

 Here's an example. The right-most table.