First, I would double-check (or maybe triple-check) that the binding is in fact set up correctly. You never know. :)
Also take a look at the BindingDescriptor.DataSourceUpdateMode property, which is used to control when data is pushed into the bound object. It defaults to "OnValidation", although in your case it may have been accidentally set to "Never". It can also be set to 'OnPropertyChanged".
Finally, if none of this works, check your debuglog.xml to see if any warnings or errors have been logged. Binding problems usually cause an exception to be thrown and not logged, but you might find something suspicious going on.
Good luck.