[macosx] JInternalFrame shadow is not properly drawn

FULL PRODUCT VERSION :
java version "1.8.0_60"
Java(TM) SE Runtime Environment (build 1.8.0_60-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Darwin Mac-mini-de-oscar.local 15.0.0 Darwin Kernel Version 15.0.0: Wed Aug 26 16:57:32 PDT 2015; root:xnu-3247.1.106~1/RELEASE_X86_64 x86_64

EXTRA RELEVANT SYSTEM CONFIGURATION :
Mac OS X El Capitan
Version 10.11

A DESCRIPTION OF THE PROBLEM :
JInternalFrame draws a gray rectangle at the bottom border of JInternalFrame instead of its shadow.

JInternalFrame is properly drawn in previous versions of Mac OS X. This issue seems to be applicable only to OS X version 10.11 (El Capitan).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
You can execute SwingSet2 demo / Internal Frames Demo.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Shadow at the bottom border of JInternalFrame.
ACTUAL -
Gray rectangle at the bottom border of JInternalFrame.

REPRODUCIBILITY :
This bug can be reproduced always.