if you have every designed a document report in NAV 2009 RDLC perhaps you opened more than one document report for copying and comparing content. (or also another report)
For example: you have finished the Quote report, and now you want to start with the Order Confirmation.
Anyway, if you have opened more than one report it was very inconvenient to figure out the visual studio layout because the taskbar doesn’t show the ID or name of the report.
This was optimized now on NAV 2013. If you have opened more than one report the taskbar shows the report ID too. (it depends on OS settings how it looks like)
Of course, if you open the same report twice or more, you have to mark it by yourself which one now is the right one, you want to use!