Earlier (until 6.0) there was an error in the program, but since then it worked. This error case was fixed with note 862838 - XK99: create new entry for 'withholding tax accounting'
I just tried it again with a slightly different way, I selected table LFBW, went to the selection screens, deselected the change tab, entered the data in the create tab, executed and got the same error that you had in the beginning.
Then I used the back button, opened the tab for fields and selected the QLAND field and executed the selection again and got this singe record that I expected.
If those ways do not work for you then you may have to contact SAP Support