The UI come to a mess when I pressed back

[veryyoung]

In the adapter I write like this
((RelativeLayout)convertView.findViewById(R.id.rl_item)).setOnClickListener(new View.OnClickListener() {
@OverRide
public void onClick(View v) {
MainActivity ma = (MainActivity)context;
ma.addMainContent(new TopicsFragment(nodes.get(position).name, nodes.get(position).getUrl(), ma.getPullToRefreshAttacher()));
}
});

public void addMainContent(Fragment fragment){
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.container, fragment).addToBackStack(null)
            .commit();
}

The UI come to a mess when I pressed back ,Is this a bug?