Editable collection with properties

Rockford Lhotka says:

"Collections do not support direct declaration of properties, so you can’t implement properties in this class. If properties are required in addition to the list of child objects, you should create an editable parent object that contains the collection, along with those other properties and their rules."

So, I decided to check this out.

I've declared simply property in my inherited BusinessBindingListBase. Somethink like this:

property long DocId { get; set; }

I can do "Fetch" and "Update". And it works. My custom property always persist.

But I'm working with 2-tier mode.

Maybe it will not work in 3-tier? What reasons could stop me from using custom properties in BusinessBindingListBase?