Why does App Store redownload already downloaded parts when resuming a paused download? Yesterday, I started downloading XCode 5.1.1 from the App Store.

I have a very slow + limited bandwidth Internet connection. It took almost 5+ hours to download 1.6GB of data. It was really late in the night, and my new MBA had been up for over 7 hours, so I "paused" the download, shutdown the MBA, shut off my modem and went to bed.

After waking up today morning, I decided to resume the XCode 5.1.1 download from App store. I figured I just needed to download another 600 MB to complete the ~2.2 GB XCode 5.1.1 download. So, I switched on the modem, switched on the MBA, opened the App Store and went to my purchases. When I hit the "Resume" download button on XCode 5.1.1 (in App Store->Purchases), the App store asked me for my Apple ID and password. I entered it and then the App Store "restarted" the download!!! All of the  1.6GB part that I had downloaded yesterday night was GONE!!!

With my metered connection, the App store now says it will take another 11 hours to download the ~2.2GB of data it needs to install XCode 5.1.1 on my MBA.

Question: What gives? What happened to my 1.6GB of already downloaded data? Is the App Store going to trouble me like this all the time in the future?
The PAUSED download is not the same as STOPPED.

You stopped the download (disconnected) so the temporary download file was deleted.

The resume function does not work for that.