The CSS property 'text-align' does not allow for a value of 'auto'. See http://www.w3.org/TR/css3-text/#text-align0
Linie 96 in TAO's drupal.css reads:
thead th { text-align:auto; }
http://drupalcode.org/project/tao.git/blob/refs/heads/7.x-3.x:/drupal.cs...
Maybe this is some kind of hack? It is ignored in tested browsers though.
Thanks!

Comments

Follow up: I tested the behavior and center or inherit is the value we want here. Since the current value is invalid this is what we actually get right now.