Strange results from DATEDIF (Month to date) if the second date changed !

Hi All,
Any one can explains the strange results from DATEDIF as decribed as follow:
In A1 and B1, I have 1st date and 2nd date.
Now I have in C1: =DATEDIF(A1,B1,"MD")
Case 1: A1=27/2/2012, B1=29/2/2012, ===> C1=2
A1=27/2/2012, B1=1/3/2012, ===> C1=5
Case 2: A1=29/4/2012, B1=30/4/2012, ===> C1=1
A1=29/4/2012, B1=1/5/2012, ===> C1=3
Case 3: A1=29/5/2012, B1=31/5/2012, ===> C1=2
A1=29/5/2012, B1=1/6/2012, ===> C1=2
In 3 cases, the 2nd date change from last date of this month to first date of next month, with 1 day different, but the difference btw 2 DATEDIF is 3 (case 1), 2 (case 2), 0 (case 3). I think the right result must be 1, which is the difference from the two 2nd date.
What is the reasonable advice should be given for this case?

Does this help...

http://www.excelforum.com/excel-form...h-datedif.html

Thanks a lot for your sharing, Jeff