Tax code can no longer be changed

What causes this issue?

If you have entered the tax code <LB>**</>, it cannot be changed, since
this code allows different tax rates in individual items.

System Response

When you acknowledge the message, the system will overwrite your input
in the field <LS>Tax code</> and replace it with <LB>**</>.

Error message extract from SAP system. Copyright SAP SE.