Table as customField in form => How to implement write through false

I have a form. One of the fields of that Form is a CustomField with inside a Table which is bound to a BeanItemContainer.
Allthough I put prsTable.setWriteThrough(false) when I enter something in one of the texfields then the changes are immediately submitted to the beans. I just want that to happen when I press confirm of the form

This is my customField class. How can I solve this?

public abstract class PrsTableCustomField<BEANTYPE extends Entity<Long>, BEANITEMCONTAINER extends PrsTableBeanItemContainer<BEANTYPE>, FIELDMAP extends FieldMap>
extends CustomField implements Initializable {

private static final Logger LOGGER = Logger.getLogger(PrsTableCustomField.class);

BEANITEMCONTAINER beanItemContainer;

@Inject
PrsTable prsTable;

@Inject
MessageSource translate;

VerticalLayout layout = new VerticalLayout();

public PrsTableCustomField() {
setCompositionRoot(layout);
}

@Override
public void setWriteThrough(boolean writeThrough) throws Buffered.SourceException, InvalidValueException{

prsTable.setWriteThrough(false);

}

@Override
public Class<?> getType() {
return Set.class;
}

@Override
public void attach() {
super.attach();
}

@Override
public void setPropertyDataSource(Property newDataSource) {

Object value = newDataSource.getValue();
if (value instanceof Set<?>) {
@SuppressWarnings("unchecked")
Set<BEANTYPE> beans = (Set<BEANTYPE>) value;
beanItemContainer.removeAllItems();
beanItemContainer.addAll(beans);
prsTable.setPageLength(beans.size());

} else {
throw new IllegalArgumentException("property needs to be a Set");
}
super.setPropertyDataSource(newDataSource);
}

@Override
public Object getValue() {
Set<BEANTYPE> beans = new HashSet<BEANTYPE>();

for (Object itemId : beanItemContainer.getItemIds()) {
beans.add(beanItemContainer.getItem(itemId).getBean());
}
return beans;
}

@Override
public void setReadOnly(boolean readOnly) {
prsTable.setEditable(!readOnly);
super.setReadOnly(readOnly);
}

public void initialize() {
String captionKey = getCaptionKey();
if (captionKey != null) {
setCaption(translate.message(captionKey));
}

beanItemContainer = getBeanItemContainer();
prsTable.setContainerDataSource(beanItemContainer);
prsTable.setTableFieldFactory(getFieldMapTableFieldFactory());
prsTable.setEditable(!isReadOnly());
prsTable.setWriteThrough(false);

layout.setSizeFull();
layout.setSpacing(true);
prsTable.setSizeFull();
setSizeFull();

layout.addComponent(prsTable);
}

public abstract BEANITEMCONTAINER getBeanItemContainer();

public abstract String getCaptionKey();

public abstract FIELDMAP getFieldMap();

protected FieldMapTableFieldFactory<FIELDMAP> getFieldMapTableFieldFactory(){
FIELDMAP fieldMap = getFieldMap();
return new FieldMapTableFieldFactory<FIELDMAP>(fieldMap);
}

@SuppressWarnings("serial")
private static final class FieldMapTableFieldFactory<FIELDMAP extends FieldMap> implements TableFieldFactory {

private final FIELDMAP fieldMap;

public FieldMapTableFieldFactory(FIELDMAP fieldMap) {
this.fieldMap = fieldMap;
}

public Field createField(Container container, Object itemId, Object propertyId,
Component uiContext) {
Field field = null;
FieldBuilder fieldBuilder = fieldMap.get(propertyId);
if (fieldBuilder != null) {
field = fieldBuilder.build();
field.setCaption("");
((AbstractComponent) field).setImmediate(true);
((AbstractComponent) field).setData(itemId);

}
return field;

}
}

public MessageSource getTranslate() {
return translate;
}
}