Try abstracting your observable collection over a private variable a private, it will work.
Replace
public ObservableCollection<Invoice> ocOpenInvoices { get; set; }
with
private ObservableCollection<Invoice> _ocOpenInvoices;
public ObservableCollection<Invoice> ocOpenInvoices
{
get { return _ocOpenInvoices ; }
set { _ocOpenInvoices = value; OnPropertyChange("ocOpenInvoices"); }
}
Please ignore this OnPropertyChange, if you have already implemented INotifyPropertyChanged in your own way, otherwise, it would be INotifyPropertyChanged that can solve your issue.