Vendor name is deleted after the approver changes the product category.

Hello,

We have implemented workflow WS14000044(Completion by Purchaser) and

WS14500015(Item-Based Main WF).

At workflow WS14500015 level, when the approver changes the product

category, the vendor name is deleted.The previous validation allows the

PO creation , But the PO is created without vendor.

Furthermore under transaction process purchase orders 'BBP_POC' the

purchaser can not access in change mode to the vendor field in order to

add a vendor.

How can we give access in change mode to the vendor field for purchaser in transaction 'BBP_POC' ?

Regards,

Lina