Start and End date calculations for Fixed membership with rollover date are incorrect

CiviMember calculates start and end dates incorrectly for fixed memberships, for certain combinations of start date, join date, and rollover date.

To reproduce on the demo site:

1) Create a membership type with duration 1 year, fixed start date of June 1, and rollover date of August 31.
2) Create a new membership of this type with a join date of January 5, 2010.

Resulting membership shows a start date of 6/1/09 and an end date of 5/31/10. But since the join date is after the rollover date, the membership should extend through 5/31/11.

Examining the code in CRM/Member/BAO/MembershipType.php, it appears that the date logic should be re-examined.