This appears to be a glitch in how I set up the append_features method for "interface modules", that causes them to forever recurse. It doesn't happen with all interfaces; I think it may only affect interfaces that extend other interfaces, or something like that. As such, I have a fix but not a test, and we must figure out a test that can work against normal JDK classes.
Fix is committed in r7671. Still open pending tests.
FYI, my case to reproduce it was:
jruby -w -rjava -e "class Foo; import Java::org.objectweb.asm.Opcodes; include Opcodes; end; Foo.new"