BAPI_PO_CHANGE cant delete funds center (fistl) value

Hello,

Im using the bapi BAPI_PO_CHANGE to modify the values of an order. The problem is, using the BAPI 'BAPI_PO_CREATE1' in testing mode to validate the parameters. If the is not cost center value, the funds center value is deleted. But when I use the bapi BAPI_PO_CHANGE I dont achieve to set the value of the field funds center as 0.

Why which the bapi 'BAPI_PO_CREATE1' in testing mode I can delete the value of funds_ctr, but when I want to save the changes in the database with the bapi BAPI_PO_CHANGE I dont success?

Thanks in adavance,

Javier.