[macos] Awt automated test "AWT_ScrollPane/Automated/ScrollPaneComponentTest" fails

Testsuite name:AWT
Test name(s):AWT_ScrollPane/Automated/ScrollPaneComponentTest
Product(s) tested:ORACLE JDK12 b28(64bit)
Test tool: tonga-4.0.2-rc2.jar
OS/architecture:mac10.14-x64

Actual behavior:
1.The test failed automatically. The details refer to ScrollPaneComponentTest.log
2.On Mac10.13 x64 with JDK12b28(64bit):Failed as the same issue.Refer to log ScrollPaneComponentTest-mac10.13.log

The detail log:
FAIL: Base Image comparison failed!
[2019-01-18T11:11:12.86] FAIL: Comparison of images after dragging the scroll bar failed!
[2019-01-18T11:11:12.89] Test failed!
[2019-01-18T11:11:12.91] About to screen capture - java.awt.Rectangle[x=0,y=0,width=1280,height=800]
[2019-01-18T11:11:16.62] Execution failed
[2019-01-18T11:11:16.62] # Test level exit status: 1