I meant a 10.7.5 Mac OS.
Have you checked for cell inset values that would cause this?
Cell styles or setting can override table settings.
If you use table styles sometimes is easy to override cell settings - select cell and do to Cell styles panel. If you see + next the name just Alt Click name of style to remove it
You should also probably turn on visibility for non-printing characters and be sure you don't have any paragraph returns or forced line breaks in the cells.