I tried building Jack using the asm-all.jar from jcenter and it failed with the same error. And when I checked the classes in this JAR it gave me "Java 1.2" as well.
So looks like the same problem applies to the upstream as well. __ This is the maintainer address of Debian's Java team <http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/pkg-java-maintainers>. Please use debian-j...@lists.debian.org for discussions and questions.