Overflow button forces Action Mode to finish

I have an EditText and I want the user to be able to select some text and apply some basic formatting to the selected text (bold, italic, etc). I still want the standard copy, cut, paste options to show, though. I read somewhere in the Android documentation that to do this, you should call setCustomSelectionActionModeCallback() on the EditText and pass it an ActionModeCallback(), so that's what I did. Here's my code:

In my activity's onCreate() method:

myEditText.setCustomSelectionActionModeCallback(new TextSelectionActionMode());

Callback declaration:

private class TextSelectionActionMode implements ActionMode.Callback {
    @Override
    public boolean onActionItemClicked(ActionMode mode, MenuItem item) {
        return false;
    }

    @Override
    public boolean onCreateActionMode(ActionMode mode, Menu menu) {
        menu.add("Bold");
        return true;
    }

    @Override
    public void onDestroyActionMode(ActionMode mode) {
    }

    @Override
    public boolean onPrepareActionMode(ActionMode mode, Menu menu) {
        return false;
    }
}

The problem I'm having is that when I click on the overflow button (to access my "Bold" menu item), the ActionMode gets closed immediately. If I set it to always show as an action, using this:

MenuItem bold = menu.add("Bold");
bold.setShowAsActionFlags(MenuItem.SHOW_AS_ACTION_ALWAYS);

It works fine and I can click on it (though it obviously does nothing). What am I missing here?

Edit: Just wanted to add that I run into the exact same problem if I actually inflate a menu instead of adding menu items programmatically. Once again, though, the problem goes away if I force it to always show as an action.