After further analysis, I concede that the directory portion of jar Pathnames should be :ABSOLUTE and not :RELATIVE. I'm not sure how long such a re-implementation will take, but it's in-progress. I'd like to get it finished before we release 0.19, but we'll see.
I'd like to preserve keeping the namestring of a jar pathname congruent to the JAR URL syntax (i.e. "jar:URL!/ENTRY") so that even when ENTRY contains an :ABSOLUTE directory, the printing of a double slash is suppressed. But whether this means I should not allow :RELATIVE directories in a jar pathname or not I am not sure. Maybe a jar pathname with a :RELATIVE directory doesn't have a namestring representation? Opinions on this are welcome.