ObservableCollection Bound from ViewModel Does Not Update View

ObservableCollection Bound from ViewModel Does Not Update View

I am allowing a user to delete an item via ContextMenu menu item within
the view, and I would like the effect to be seen automatically in the
view. As of now, the item in the view remains until the app is restarted,
in which case it is then no longer visible. This is very confusing to the
user who believes the item has been removed completely from the
application. My question is, what am I doing wrong that would fix this
issue?
App.xaml.cs
//PictureRepository is a class that gathers pictures from IsolatedStorage
public static PictureRepository PictureList
{
get
{
return PictureRepository.Instance;
}
}
PictureRepository.cs
#region Constants
public const string IsolatedStoragePath = "Pictures";