davoscollective (5/29/2012)
I'm not sure if a page at simple-talk from 2006 qualifies as a good reference, although BOL has its fair share of errors anyway so probably not worth worrying about.
I had the same concern, so I tested it (on SQL2012). I did indeed get an error message when trying to do a differential backup of master. (And I also got an error message when trying the same on tempdb). Note that I did not test if the other databases do indeed allow the differential backup.