Another interesting development, a coworker was able to adjust the table borders easily in Word 2013 (I'm using 2007). She just selected the border on the shifted cells, dragged it into position, and it didn't move any of the other cells.

BUT the resulting file does not show up properly in 2007 or 2010. The cells are still shifted when opened in these versions (and continue to shift with any other adjustment).

I was able to have minor success in removing the left cell margin from some of the affected cells/rows, then reapplying it, and in some cases that fixed that row. but it doesn't seem to be consistent. Also, I found that when this issue occurs, it increases the table width past 100% on each edit, which I can then reset. Unfortunately, the rows that are shifted are also set to 100%, and are wider than the actual table.