Make sure that the document default font size matches the font size of your Normal paragraph style. This is necessary for the settings in the table style to work properly (although it sounds completely unrelated).
To change the document defaults, do the following: In the Styles pane (Ctrl+Alt+Shift+S), click the Manage Styles icon. On the Set Defaults tab, change the default font size to whatever size is defined for your Normal style. Click OK. (Alternatively, you can of course change the font size of the Normal style so that it matches whatever is the current default font size.)