What does the second parameter in ACCRINT do?

[Boris]

I'm a bit confused what the second parameter in ACCRINT does. Microsoft has
documented the calculation of ACCRINT at
http://office.microsoft.com/en-us/assistance/HP052089791033.aspx but the
second parameter doesn't appear in the formula. Furthermore the calculation
of ACCRINT was changed somewhere between Excel 97 and Excel 2003:
http://support.microsoft.com/kb/904826/en-us

I use Excel 2003. Is the second parameter in ACCRINT now deprecated? It
doesn't seem to affect the calculation most of the time. However when you
enter some special dates you get weird results. Try for example
ACCRINT("1/1/2000", "2/28/2000", "12/31/2000", 0.01, 100, 1, 0) and
ACCRINT("1/1/2000", "2/29/2000", "12/31/2000", 0.01, 100, 1, 0) - they don't
return 1. Is this a known bug or is there something I don't understand about
ACCRINT?

Boris