Time-dependent master data and Multiplanning Area

Hi,

I'm using a Multiplanning Area for planning data for this year as well as next year. This MPA consists of 6 Planning areas.

Cost center texts or attributes can be different this year and next year, so i need to use the Key date field on the master data tab of the planning area.

The question is: which of the underlying planning areas will the system read to get the key date from? From what I could see, it's taking the first Planning area from the list (when looking at the MPA definition) and disregards the others.

Does someone know the exact logic in this area?

Many thanks,

Olivier