[Q] XPeria P-LT221 - how to UNROOT? topic

I rooted my Xperia L-LT221 with this method: http://forum.xda-developers.com/show....php?t=2023756. Basically, it does this with a Flashtool:

- Flash 6.1.B.0.599_Kernel via FlashTool
- Reboot then run Root_with_Restore_by_Bin4ry
- Flash 6.1.1.B.1.75_Kernel via FlashTool

I have root, because Titanium Backup works.

Now I am trying to UNROOT the phone. I connected the phone to my PC and run Flashtool. Selected Root --> Unroot and I was prompted that my device was "NOT ROOTED".

How can I unroot the phone? I am trying to go back to factory state.

Model: LT22i
Android: 4.0.4
Baseband: u8500-49020908-P2H_EC01
Kernel: 3.0.8+ (stock)
Build: 6.1.1.B.1.54