The following unit test is failing on WIndows platforms:

$ gradle -PFULL_TEST=true :fxpackager:test

com.sun.javafx.tools.ant.FXJarTest > capitalInManifestTest FAILED
    String index out of range: -8
        at com.sun.javafx.tools.ant.FXJar.execute(FXJar.java:152)
        at com.sun.javafx.tools.ant.FXJarTest.capitalInManifestTest(FXJarTest.java:115)

        Caused by:
        java.lang.StringIndexOutOfBoundsException: String index out of range: -8
            at java.lang.String.substring(String.java:1918)
            at com.sun.javafx.tools.packager.PackagerLib.jar(PackagerLib.java:731)
            at com.sun.javafx.tools.packager.PackagerLib.jar(PackagerLib.java:655)
            at com.sun.javafx.tools.packager.PackagerLib.packageAsJar(PackagerLib.java:267)
            at com.sun.javafx.tools.ant.FXJar.execute(FXJar.java:150)
            ... 1 more

This is a regression, likely introduced by the fix for RT-39974.