One thing hard learnt regarding Dependency Properties

I was scratching my head like crazy on this one but could not figure it out. It turns out that: if you put a default value of reference type in the Register function of DependencyProperty, this vaue will be shared by ALL instances of the property and cause problems. For example, if you have a property of the type Collection, then all data added to that collection will "magically" show up in other instances too! This has bothered me for a long time and I finally found a good explaination at this web page.