Product Tested : JDK 8u341 b32
Platform Tested : Windows 10 Pro
Is it regression : No
Reproducible: Always
Test result on the last GAed release for this train:
         Fails With JDK 8u341b10 , JDK 8u331b09 , JDK 8u321b07 , JDK 8u40b27
           Same StringIndexOutOfBoundsException along with NPE in case of TextArea
           Same StringIndexOutOfBoundsException along with IAE in case of TextField

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) Start attached test Main. .
2) Start Narrator ( Win + Ctrl + Enter)
3) In Textarea enter large text and start deleting by continuous Backspace key Press (i.e Pressing BackSpace Key and not releasing until some time)
   Testing with TextField Component also produces the same exception.

Exception Log :

/cygdrive/c/work/repos/java_installations/64bit/jdk1.8.0_341b32/bin/java -showversion Main
java version "1.8.0_341"
Java(TM) SE Runtime Environment (build 1.8.0_341-b32)
Java HotSpot(TM) 64-Bit Server VM (build 25.341-b32, mixed mode)

Exception in thread "JavaFX Application Thread" java.lang.StringIndexOutOfBoundsException: String index out of range: 19
        at java.lang.String.substring(String.java:1963)
        at com.sun.glass.ui.win.WinTextRangeProvider.GetText(WinTextRangeProvider.java:355)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.lambda$null$4(WinApplication.java:185)
        at java.lang.Thread.run(Thread.java:750)
Exception in thread "JavaFX Application Thread" java.lang.StringIndexOutOfBoundsException: String index out of range: 16
        at java.lang.String.substring(String.java:1963)
        at com.sun.glass.ui.win.WinTextRangeProvider.GetText(WinTextRangeProvider.java:355)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.lambda$null$4(WinApplication.java:185)
        at java.lang.Thread.run(Thread.java:750)