On your demo and on my old version when I select an item in the editor that matches the fontname or fontsize the appropriate item in the fontname or fontsize dropdown is selected.
However if I follow the instructions for modifying common.config the dropdowns no longer automatically select when i select an span in the editor. The only items that work are the ones the use the value equal to an integer. If I set the value to something like 12pt or 12px it correctly puts the size in the text but does not select it in the dropdown.
This is a sample of the common.config:
<
FontSize>
<item text="[[NotSet]]" value="null">
<html><![CDATA[[[NotSet]]]]></html>
</item>
<
item text="1 (8pt)" value="1">
<html><![CDATA[<span style=font-size:8pt>8pt</span>]]></html>
</item>
<item text="10pt" value="10pt">
<html><![CDATA[<span style=font-size:10pt>10pt</span>]]></html>
</item>
<item text="12px" value="12px">
<html><![CDATA[<span style=font-size:12pt>12px</span>]]></html>
</item>
<item text="4 (14pt)" value="4">
<html><![CDATA[<font size='4'>Size 4 </font>(14pt)]]></html>
</item></FontSize>