In the RadPivotGrid:
Open the Label Filter dialog on a dimension, don't set anything and press OK, then all items are present and nothing is filtered out as expected.
Open the Label filter again and manually specify that the value must equal "xyz" and click OK then it will exclude every item that doesn't match this. Again, this behaviour is what you'd expect.
If you then open the dialog, and delete the "xyz" from the textbox so that the dialog appears exactly as it did originally, and click OK then you won't see any items in your pivot grid. This is because it is now filtering out anything that doesn't have an empty string as the label. This is not what I'd expect.
To remedy this, you can click on the dimension and see that the Label filter is still ticked in the context menu, and click "Clear filter", but this isn't exactly intuitive. 
I'd like the filter to be cleared when you clear the text in the box.