Bug Report: This has been an issue as far back as I can remember. It's in Toast 11 for sure maybe prior to that. I was hoping it would be corrected in Toast 14 but no dice. If the Toast team sees this report would you please add this to your bug list.
1. Setup a UDF Data disc (blu-ray HDMV in my case) and burn.
2. Upon completion Toast will update the size of the files to be burned, but at double the correct/original size.
3. You can't clear the miscalculation by removing the content and adding it again. You have to close Toast, restart the app and setup the disc again.