[Q] [Need help] Z C6602 Camera problem topic

hi guys, i've recently recieved a Xperia Z C6602 as present
been using it for a couple week now
great phone, however
just a moment ago, i was tried to take some night photo shots
and found a small problem with the camera
hope if anyone could help me, coz it's kind of annoying

the HDR and all the other function seems to work fine
photo under auto ISO setting is no too bad
however with the manual ISO setting (with or with out HDR engaged...)
i have found that the displayed image on the phone screen before photo taken, from ISO 100 ~ ISO 400
is actually much darker then the actual photo taken!
but the ISO 800 ~ ISO 1600 seems to be with out this issue (and ofcoz auto ISO also do not have this problem)

for example
[ISO 100]



[ISO 200]



just wondering if anyone have the same problem?
is this a bug for the camera? or is this normal?
i had a bit of look online but didn't find much in regard to this issue
tried to play with the setting, changing the photo size, still didn't help

i really love taking photos
was using HTC ONE MINI before this
and changed to Z now with much higher res, it's awesome
but this problem with the display before taking photo is actually very annoying
for that, i can not see clearly, and predict the outcome of the photo this way

can anyone please help?