QMessageBox customized buttons aren't displayed

Non-standard buttons on a MessageBox aren't displayed. I'm using the default for Android Native Dialogs. In the code below, I can't see the "More" button in the message box on Android, but it looks fine on the Desktop.

QMessageBox mb1;
mb1.setText("Why can't I see the More button?");
mb1.setStandardButtons(QMessageBox::Ok);
QPushButton *qt = mb1.addButton("More...",QMessageBox::HelpRole);
mb1.exec();