I am not the expert on this, but this was a little information I was given a while ago.
When the download of your patch is interrupted, it is normal for the patcher to say it is scanning files/ calculating differences. This is because when you interrupt a download, the patcher doesn't know exactly where it was stopped; the program itself was terminated, so it needs to spend sometime to figure out where it was stopped; this is why sometimes you see the 33% and calculating files. When that happens, DO NOT interrupt it. If you do interrupt it, the system needs to redetermine it's download progress and will scan the file again. I highly recommend just being patient and letting it patch / do its thing, if it gets stuck (both the file scanning and the download progress %), then let us know.