... not exactly sure..

For example:
I download a file that's 2mb & another that is 4mb...
After you finish downloading, you will see (at search) that you downloaded all these files that arent the same file size or length. [2.5mb, 3mb,...]

I noticed this when I went back to download a different file, the original length was about 4:25 min., but I had alleged downloaded one that was 3:30...
This may be due to fragments.

Then again, this is my hypothesis...

I bet that if you go back and search any files you've already downloaded (such as music)... you'll see this...