ListView's attached properties ListView.*section don't always return what they should.
ListView.nextSection first updates to the right next section ("Tiny") and then goes back to the wrong empty string.

The weird thing that even seemingly unrelated things can turn this behavior on/off, for example, in the attached file you can "fix" it be changing the Window back to being Rectangle.

With Rectangle as root element you get: https://pastebin.com/hCr8ZbXk  (correct) 

With (as attached) Window as root element you get: https://pastebin.com/aRC2kUTu

The first element gets the right 2 updates, then it gets a third one which resets nextSection to empty string