What does the 2nd BD scanning bar do?

Using DVDFab, LG GGWH20L, Windows 7 RC.

Making a backup copy of Blu Ray “Paul Blart Mall Cop”.

After DVDFab makes the initial scan when you first open DVDFab (Main Movie mode ) I get to uncheck all the items I don’t want so it could fit on a BD-R 25gb disc. Right after all my unwanted items are unchecked a 2nd smaller scan bar appears at the bottom of window right under Quality: 100% (22,113gb…

This scan takes about 4 - 5 minutes. My question: What is the purpose of this 2nd scan?

 Thank you