Billing plan factory calendar special rules (query)

SAP SDN Forum:
https://www.sdn.sap.com/irj/sdn/thread?threadID=385881&tstart=0

Sapfans:
http://www.sapfans.com/forums/viewtopic.php?t=282353&highlight=

http://www.sapfans.com/forums/viewtopic.php?t=283357&highlight=

Problem:

I've created a factory calendar and have assigned it to a billing plan type and the customer master record. In the factory calendar, under special rules, I've specified the billing dates as:
15.04.2007
30.04.2007
15.05.2007
31.05.2007

When I create a contract with start date 10.04.2007 and end date 05.05.2007 the billing dates in the billing plan are determined as follows:
15.04.2007
30.04.2007
05.05.2007 (not 15.05.2007 as I expected)

In other words the last billing date is the end date of the contract and not the date I have specified in special rules. How is that date determined? I want the last billing date to be the 15th, or the end of the month as specified in my special rules. I've included some screen shots of the poroblem and the settings.

1. Create contract

2. Display billing plan

3. Configuration

3.1 Billing plan type

3.2 Date Determination rules




3.3 Factory calendar