Post (Not a Noob)Xperia u not getting rooted .10 kernel

Hello, thank you taking your time.

I Have flashed rooted modified many sony and samsung devices including 2 XUs before but this one does not get rooted in ICS.

I got a XU of a colleague running GB and I updated it to ICS .B.100 firmware. and for root, as usual method flashed .10 kernel and flashtool also stated boot loader status as rooted. but I cant get SU binary or superuser or supersu into the system using flashtool root or Doom-Lords batch file. all stops with 6..1.B.100 not supported even I have already flashed .10 kernel. So I checked build number on settings and it also stating .100 even flash tool successively flashed .10 . Then I tried manually push SU binary via adb and it soft bricked the phone. I cant understand what else I can do here. all adb drivers, s1 fast boot drivers, adb commands, fastboot commands all working perfectly. can somebody help me with whats going on here?

thank you again.
Note: Boot loader unlocked.