Okay ... so where is the real file the symlink points to (what directory)? And do you get any errors at all? Looking at the code I see attempts to symlink if the file being extracted has a file mode setting indicating it's a symbolic link. There's a warning if that fails. Can you easily check the file mode settings and see if the file that ends up in the archive has the symlink bit set?

Looking at the code, I can see they do (on UNIX) a -l check when the file is added; set a SYMLINK file type and save the file its linked to if that's set; then try to call symlink if they see the SYMLINK entry type during extraction using the saved values. The reason I think you'll have problems with relative path names is that I don't see any path information being stored with the link name ... not sure if that matters if it's relative since you'd want it relative on the way out? I'd need to see what directory they think they're in though ...

If you have access to the source and can modify it I'd probably just copy it and put some debug in there. It may make it very clear with a smaller amount of effort than debugging around the module.