Kindle Touch: Diagnostics Mode not working

Hi,

following the instructions posted here, I created a file called ENABLE_DIAGS within the top folder of my kindle and restarted the device (Menu > Settings > Menu > Restart). According to the instructions my kindle should now start in diagnostics mode, but unfortunately it's still in "normal"-mode.

Device info:
Model: Kindle Touch
FW Version: 5.3.2.1 (1840090002)

My kindle has not been jailbroken before, this is the first time I try to "costimize" it.

Is it possible that they switched off the possibility of entering the diagnostics mode with the latest version 5.3.2.1?
What am I doing wrong, how can I enter diagnostics mode anyway?

Thanks for your help,
Dante