I have tried to run your code and it works ok on my machine.
I have VFP 7.0


>I have the following code in a prg
>
>

SELECT TableA
>ZAP
>
>SELECT * FROM TableB INTO CURSOR C
>
>SELECT TableA
>APPEND FROM DBF('C')

>
>Cursor C contains the following
>ID VALUE
>------------
>1 Task 1
>2 Task 2
>3 Task 3
>4 (empty)
>
>After the append statement TableA contains the following
>ID VALUE
>------------
>1 Task 3
>2 Task 2
>3 Task 3
>4 (empty)
>
>Can anyone see my mistake?
>
>Thanks in advance.