How to set work center in Service Order created from Sales Order?

Hi everyone,

Please let me describe my current scenario:

I have created a Sales Order with two items and both of them have provoked the system to create an associated Service Order, which matches the richt and expected behaviour.

First service order them has been associated to Work Center 'A' while the second one has been associated with Work Center 'B'.

Materials are both the same type and there is no difference at all between the two items in the Sales Order.

I have checked unsucessfully all cusotmizing points in order to discover the key about this strange behaviour.

I would be very grateful whether someone could help me to figure out how can this be possible? I mean, why the two Service Orders hasn't been associated to the same work center?

Which are the customizing points to define the parameters of a service order that is created straight from sales order?

Thanks a lot in advance and best regards.