Tracking Entries in Prod. Order are deleted after Planning

Hi,

I'm facing following problem (Dynamics NAV 2009 SP1):
1. out of a planning worksheet line the production order is created (carry out action message)
2. Order tracking lines are created automatically between sales order and production order
3. in the released production order, at the beginning, item tracking lines for serial no. are created manually
4. A new Calculate plan in the Planning Worksheet is running

--> Result: all of the item tracking entries in the production order with my serial numbers are deleted.

Reservation functionality is not possible for my customer.

Does anyone have a solution for this.

Thanks and best regards
Harald