How can we set the radio button R[Component backflush] on MFBF transaction?

In this case, the SAP application checks the cursor position (instead of the value of the radiobutton) and then sets the radiobutton. Normally it is not done this way. If you change your InputScript to

Screen SAPLBARM.0800

Set R[Component backflush] "X"

SetCursor R[Component backflush]

Enter "=RBTYP"

it will work.