MACROMEDIA FLASH MX 2004-USING COMPONENTS Use Manual page 723

When a style's value is not inherited, you can set its style only on an instance, not on a custom or
global style sheet. A style that doesn't inherit its value is set on the class style sheet, and therefore,
setting it on a custom or global style sheet does not work.
Example
The following example registers as an inheriting style:
newProp1
StyleManager.registerInheritingStyle("newProp1");
StyleManager class 723