Please describe the problem:
When an image is set on a button (using gtk_button_set_image), the button ignores the user_underline setting.

Steps to reproduce:
1. gtk_button_set_image(...)
2. gtk_button_set_label(...)
3. gtk_button_set_use_underline(..., FALSE)


Actual results:
the _ is always treated as a mnemonic specifier

Expected results:
no mnemonics show up in the button label

Does this happen every time?
yes

Other information:
Here is the relevant code in gtk_button_construct_child(), with added commentary and the irrelevant bits elided:

  if (image)
    {
      ...

      if (label_text)
	{
          // doesn't check for use_underline >:(
	  label = gtk_label_new_with_mnemonic (label_text);
	  gtk_label_set_mnemonic_widget (GTK_LABEL (label), 
					 GTK_WIDGET (button));

      ...
	}
      
      ...

      return;  // <--- Early return!
    }
  
  if (button->use_underline)  // <--- This check not reached
    {
       ...
    }