ScrollBar sometimes show up incorrectly.

REPRODUCE :
1) Compile the sttached .java files
2) Launch "java Frame1"
   You will see a whindows having "show Dialog" button.
3) Click "show Dialog"
   you will see a dialogue box having "close" button.
   You may not see scrollbar in the dialog at this step.
4) Click the "close" button.
5) Click "show Dialog" at step 3)
   You will see scroll bar in the dialog.

PROBLEM:
 The list in the dialogue does not have so many items(Row 1,2 ...6).
 Also, the dialogue is big enough to show all the items without
 scroll. So, scroll bar is not needed at step 5),(see expected-dialog.jpg)
 but actually scroll bar shows up.(see actual-dialog.jpg)

CONFIGURATION :
  JRE : 1.4.2_07/5.0u3/6.0b54
  OS : WindowsXP(SP1, Japanese)