Restrict Withholding Tax change in not cleared documents

Hello,

We want to adjust the Document chnage rules - OB32 in a manner that it restricts Withholding Tax fields from changing when the document is not cleared.

We tested & found that the Withholding tax fields as below when defined in document change rules are giving strange results.

BSEG-QBSHB Withholding tax amnt

BSEG-QSFBT Wthld.tax-exempt amt

BSEG-QSSHB Withhold.tax base

BSEG-QSSKZ Withholding tax code

BSEG-QSZNR Exemption number

Of these the field BSEG-QSZNR - Exemption number field remains unmodifiable in FB02 when the document is cleared & also when it is not cleared. We tested it for Vendor & the settings were made for Account type K.

The field is always greyed out even if we make the field as modifiable in OB32.

The rest of the fields are remaining modifiable when the document is not cleared & become non modifiable when the document is cleared. This behaviour is not affected by whatever settings we make in OB32.

We tried to search for an SAP note for this peculiar behaviour but could not find one.

Could you please help.

Thanks & Regards

Shreenath