According to WPF/Silverlight (at least I think this is the way it is suppose to work). When figuring out what value a property has
1) Local value
2) Style setters
3) Property Value Inheritance (up the element tree)
4) Default value
In WPF their are other precedences eg. template triggers.. etc...
Silverlight seems to put Property Value Inheritance ahead of Styles as demonstrated in the snippet below. The FontSize property is controlled by the setting on the UserControl and not from the Style definition.
<UserControl x:Class="TextBlockWithStyleStarter.Test"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Width="400" Height="300" FontSize="24">
<Grid x:Name="LayoutRoot" Back ...
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