Kristof,
Great question! I was stumped on that myself.
The answer can be found in the JLS at
15.8.4 It's a 'qualified this' reference. An enclosed class can refer to members of it's enclosing class via <Enclosing Class Name>.this.<member>
Interestingly enough, the depth of the inner class doesn't seem to matter:
o/p:
I : false
II : true
II : false
Thank You