[JSF2] f:ajax doesn't seemed to decode input field

composite xhtml code

component java class code

@FacesComponent("intac.web.UIStatus")
public class UIStatus extends UINamingContainer implements Serializable {

private static final long serialVersionUID = 1L;
    private int delta;

private String getName() {
        return getAttributes().get("name").toString();
    }

private StatusValue getValue() {
        return (StatusValue) getAttributes().get("value");
    }

public int getNeedPoint() {
        return getValue().getNeedPoint(delta);
    }

public int getDelta() {
        return delta;
    }

public void setDelta(int delta) {
        System.out.println("delta=" + delta);   // DEBUG CODE
        this.delta = delta;
    }

public String getDisplay() {
        return String.format("%d+%d", getValue().getUnmodified() + getDelta(), getValue().getModifier());
    }

public void modifyDelta(ActionEvent ev) {
        String cmd = ((UICommand) ev.getComponent()).getValue().toString();
        if (cmd.startsWith("+")) {
            cmd = cmd.substring(1);
        }
        int ddelta = Integer.parseInt(cmd);
        delta += ddelta;
        if (delta < 0) {
            delta = 0;
        }
    }
}

When I click button, AJAX request goes to container, and it should call setDelta, but it doesn't.

Am I do something wrong?