Did you try to use the x:Shared
attribute?
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Button x:Shared="False" x:Key="buttonResource" Content={Binding BoundText}/>
</ResourceDictionary>
For more info read here.
In case this does not work, you can store a template in your resource, instead of the button and use a ContentControl inside your window to display it.