1. If you have filtered RadGridView, you can access the filtered data through its Items property -- this will give you only the items that are currently visible.
2. RadGridView.FilterDescriptors.Clear() is the correct way to do it. It will not leave any UI indications as demonstrated in the sample project that I have attached.
P.S. The "Select All" check-box might be left in indeterminate state (i.e. a dash), but we have logged this bug and will fix it as soon as possible.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.