I've already noticed that factory reset format internal memory (=SDCard).
but never had problem with external SDCard
Why does doing a factory reset or formatting /data within CWR format the sdcard? In every android device I've owned with CWR, doing a factory reset and does not format your sdcard. And when you specify to only format /data it should only format that directory.
I've flashed/rooted/tinkered with many many android devices with CWR and have never had this issue of it constantly formatting the sdcard. Does any one else have this problem?
It was a bug due to a symlink between /data/media and /sdcard that caused the internal sdcard to be wiped every time. There was an updated version here that fixes the problem. It does not work on ROW tablets though. I don't know if there is a ROW version with the fix, but maybe you could ask realyst2k if he could incorporate the patch that was used on the other version.