Third tone sandhi: when (if ever) does 3 3 become 3 0 instead of 2 3?
"bao3 bao0" is actually not a third tone sandhi here. 

It is because the tone of second bao3 got neutralized.   

Usually a second character of a two-character word would get neutralized, I would say it is a accent thing that depends on people from different places of China.