In the article you linked to, engadet claims WP8 supports "true background multitasking". That is a false statement.
Originally Posted by Zolotoy
WP limits multitasking to a specific set of features implemented by the OS. In that same article, engadget mentions two of these features, namely "VoiP" and "Location". These are the features WP8 can process in the background:
- VoiP (continue streaming voice data packets, even if a VoiP app, such as Viber or Skype, is in the background)
- Location (maintain a GPS fix, even if a location aware app, such as Nokia Drive, is in the background)
- File Transfer (continue up- or downloading files, even if the app doing so is in the background)
- Audio (continue playing audio, even if the media player is in the background)
Restricting background processing to these features is an intentional limitation, which is why WP8 can't be claimed to support "true background multitasking" or "real multitasking", as that usually implies multitasking of two or more entire apps.
Although WP apps can transfer files in the background, that doesn't mean they necessarily will. This only occurs if an app explicitly "asks" the OS to process such a file transfer operation in the background. Failing to do so (intentionally or unintentionally) will cause the OS to interrupt the file transfer operation as soon as the app is relegated to the background (any WP app is suspended at that point and no longer has access to the CPU). An app that is suspended in such a fashion will resume file transferal only after it is brought back to the foreground.
The situation you described, where a file transfer is "restarted", sounds like a bug. Possibly the file transfer is resumed correctly but only the progress bar is screwed up?