Include with explicit encoding doesn't work

[chkpnt]

I've an ISO 8859-1 encoded file, which I'm Including like this:

[source]
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include::assets/application.properties[encoding=iso-8859-1]
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This works fine with IntelliJ Plugin AsciiDoc v0.39.7 and on the command line with Asciidoctor v2.0.20. But it doesn't when using the Gradle plugin v3.3.2, which gives me an AsciidoctorCoreException ("Failed to load AsciiDoc document - invalid byte sequence in UTF-8").