src/java.desktop/share/classes/javax/swing/plaf/metal/MetalButtonUI.java

*** 235,243 ****
          }
          else {
              /*** paint the text disabled ***/
              g.setColor(getDisabledTextColor());
          }
!         SwingUtilities2.drawStringUnderlineCharAt(c, g,text,mnemIndex,
                                    textRect.x, textRect.y + fm.getAscent());
      }
  }
--- 235,243 ----
          }
          else {
              /*** paint the text disabled ***/
              g.setColor(getDisabledTextColor());
          }
!         getTextUIDrawing().drawStringUnderlineCharAt(c, g,text,mnemIndex,
                                    textRect.x, textRect.y + fm.getAscent());
      }
  }