CM11 M12 Available storage problem topic

Guys, I'm new to this forum and I need your help.

I've flashed a CM11 SNAPSHOT M12 on my Samsung galaxy s3(international version) CWM 6.0.4.6 touch just two days ago. And when i look at my storage, it says:
Total space = 11.35 GB
Available = 1.50 GB
Apps = 1.51 GB
Pics & Vids = 6.78 MB
Downloads = 43.35 MB
Cached data = 149 MB
Misc = 2.34 GB

As you can calculate it, the Used space doesn't match with the Available storage.

So, what's taking my internal storage so low? Because i don't have any hidden files installed/saved on phone.
FYI: Before flashing the CM rom, I've already made a NANDROID backup; but it's saved on external sd card.