src/java.desktop/macosx/classes/com/apple/laf/AquaButtonUI.java

*** 413,423 ****
              g.setColor(b.getForeground());
          } else {
              /*** paint the text disabled ***/
              g.setColor(defaultDisabledTextColor);
          }
!         SwingUtilities2.drawStringUnderlineCharAt(c, g, text, mnemonicIndex, localTextRect.x, localTextRect.y + fm.getAscent());
      }
  
      protected void paintText(final Graphics g, final AbstractButton b, final Rectangle localTextRect, final String text) {
          paintText(g, (JComponent)b, localTextRect, text);
      }
--- 413,425 ----
              g.setColor(b.getForeground());
          } else {
              /*** paint the text disabled ***/
              g.setColor(defaultDisabledTextColor);
          }
!         getTextUIDrawing().drawStringUnderlineCharAt(c, g, text, mnemonicIndex,
!                                                      localTextRect.x,
!                                                      localTextRect.y + fm.getAscent());
      }
  
      protected void paintText(final Graphics g, final AbstractButton b, final Rectangle localTextRect, final String text) {
          paintText(g, (JComponent)b, localTextRect, text);
      }