Hi,
What is the nature of the commitment item deriving through inventory GL. Means commitment category and transaction type.
If it is 30/3, it will consume budget and you have to write a new derivation rule. You can take the reference of other transactions also in which inventory account is hitting. How in those transaction system is deriving fund center. There are many inventory transactions, in which system does not require cost center.
If it is 40/3 nature, system will not consume budget. You can derive dummy like fund center in this type of case.
Its all about derivation setting.
Regards,
Ankit Agarwal