Dialog border color can be seen, when the dialog is move over the textarea scrollbar (horizontal & vertical) intersection point.

Step to reproduce:
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1) Run the attached program. You will see a frame.
2) Type some characters in the textarea, so that you can see horizontal scrollbar.
3) Click on the 'Click Me' button. you will seee dialog.
4) Move the dialog on the textarea scrollbar intersection point . Observe that dilog border color (blue color) is seen on the textarea scrollbar intersection point. If you see the same ,then the bug is reproduced.

I have attached the screen shots of the same.
This happens on the native application also ( notepad), but the border color (blue color) is not seen, instead textarea scrollbar intersection color is seen.

I tested this in 1.4.2 to Mustang b85.