Styles in OOo appear to be set up along the same lines as CSS -- styles can be
based on other styles, and alterations to base style definitions cascade down to
dependent styles.  This makes sense; it's how CSS works, it's how MS Office
works, and it's how OOo works -- for paragraph styles.  

However, for character styles, things can get a little funny.  Select some text
and set it to a certain character style.  Then manually change the character
style, perhaps add underlining, and click New Style from Selection on the
Stylist.  Name the new style.  Now right-click the parent style name in the
Stylist, choose Modify, and change the font.  The change will not be reflected
in the dependent style.

Look at its details of the dependent style by right-clicking its name on the
Stylist and choosing Modify.  The Organizer tab will show that the new style is
correctly based on the character style we first set the text to.  However, we
can also see that the new style definition is far too specific.  What we expect
is that the definition will *only* include those differences from the *parent*
style, but instead the definition includes all differences from the _default_
style, which is clearly an error.  Consequently, changes to the parent character
style definition may not be propagated to dependent styles.  

However, if we create the dependent character style by right-clicking the parent
style in the Stylist and choosing New, instead of using New Style from
Selection, the dependent style definition is as we expect -- it only includes
those differences from the parent style, and any changes in the parent
definition are reflected in dependent styles.