<DockPanel   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
		    <DockPanel.Resources>
        <Button  x:Shared="False" MinWidth="20" MinHeight="20" x:Key="redButton" Background="red"/>
    </DockPanel.Resources>
    <ListBox >
        <ListBoxItem Content="{StaticResource redButton}"/>
        <!--drugie wywołanie redButton teraz już działa-->
        <ListBoxItem Content="{StaticResource redButton}"/>
        <ListBoxItem>Element1</ListBoxItem>
    </ListBox>

	</DockPanel>