Ordinal Dates

Hello all PP members;

I have a problem when creating ordinal dates in P3, i hope anyone of
you can assist:

[Question] Let say the project start on 15 Jan 2006, so, by right the
ordinal date for the project is:
15 Jan 2006 - 15 Feb 2006: Month 1
15 Feb 2006 - 15 Mar 2006: Month 2
15 Mar 2006 - 15 Apr 2006: Month 3
15 Apr 2006 - 15 May 2006: Month 4

But P3 show me the following, which is incorrect:
1 Jan 2006 - 31 Jan 2006: Month 1
1 Feb 2006 - 28 Feb 2006: Month 2
1 Mar 2006 - 31 Mar 2006: Month 3
1 Apr 2006 - 30 Apr 2006: Month 4

Any idea?

Kind regards

Marcio Eduardo
Rio de Janeiro - Brazil