Serious bug with storage space reporting

[AC Question]

I'm using Marshmallow on Android One device. The total internal storage reported is 2.23Gb of which 1.79Gb is being used. It shows Apps only take up 896Mb and cache is 1.20Mb ( I cleared the cache). What could be taking up the remaining space?
Please take a look at the screenshot provided in the link below.

s28.postimg.org/5p613igsd/Screenshot_20160320_124034.png