RadDataPager/RadGridView refresh

Trying to get a RadDataPager with a RadGridView to update the list of items when the underlying bound collection changes. I have RadDataPager.Source bound to a property in the viewmodel, and RadGridView bound to PagedSource of the pager. The collection doesn't actually implement any events for changing, so what I'm doing is replacing the value of the bound property with a new collection. I have verified it is a new instance, and that INotifyPropertyChanged is being raised. However the gridview isn't updating until I move to another page, and then move back. I'd expect the datapager to detect the underlying collection has changed, and instruct the gridview that the current page's contents have changed. It doesn't.

What might I be missing?