liability account in AP invoice is being Overriden even the supplier site Liability account is null

Summary:

When creating invoice, the liability account is the default liability account, but when invoice is validated, the liability account is overwritten to a different account, even though there is no Liab account in Supplier Site.

Is there other overwritting rule that in SLA that can override the Liab distribution?

Content (required):

I Also populated the Liability account in Supplier Site, the account is being defaulted in the AP Invoice when creating, but then gets override when I validate the Invoice, it is getting the IC Balancing Rule account. But our requirement is, it should get the liability account from the Supplier site, not the IC balancing account.