Additional info:
MacOS 11 Big Sur, 64 bit

Tested on
JDK15b36 and JDK11b28

Steps to reproduce :

1) Run testcase using jtreg.
2) Bottom line looks like a single line. please see attached image(actual.png)

Actual behavior:
The bottom line dont touch the right line in the rectangle.

Expected behavior:
Please see attached image (expected1.png)