Budget availability check for Prim.costs in Network Activity

Hi,

When costs are planned in internal & external processing in the network activity, the budget check happens correctly;

However when we plan costs in the tab ' Prim.cost' for a particular cost element  in the network activity, it is not subject to budget availability check;Is this a standard behaviour or some config steps are missing ?

We have not maintained any exemption of cost element for availability control;  Appreciate any suggestion. Thanks