The painting is not happening properly after changing the look & feel from Java look & feel to Motif look & feel . And from GTK look & feel to Motif look & feel. Feel like an extra component ( look like a thick line is draw ) is added to JScrollPane (before the scroll bar ) in Motif look & feel.

I have used SwingSet2 to demonstrate this problem.
1) start SwingSet2.
2) select JScrollpane demo button.
3) Select Motif look & feel. Observe thirdimage.PNG file( i have drawn the
           circle). you can see like a thick line is draw before the up & down arrow.
4) Select GTK look & feel.
5) Once again select Motif look & feel . Observe fourthimage.PNG file ( i have
           draw the circles). you can see the think line is still bigger when compare to
thirdimage.png file. And even it has broken the corner images also. I have draw a red line near the down arrow b/c the down arrow is not painted properly.
 
  While testing the above step 5 . you can observe that the corner image actually breaks in GTK tool & feel. which also results in Motif Look & Feel.

To ensure this i have taken another application of JScrollPane in the same SwingSet2 application. Where JList is using JScrollPane.
1) start SwingSet2.
2) select JList demo.
3) Select Motif look & feel. Observe firstimage.PNG file(i have drawn the circle). you can see like a thick line is draw before the up & down arrow.
4) Select GTK look & feel.
5) Once again select Motif look & feel . Observe SecondImage.PNG ( i have draw the
           circles). you can see the think line is still bigger when compare to
           firstimage.png file.

I tested this with build 64 in mustang & in tiger rc build 63 it results same.