Comment 1 for bug 723964

What's causing this is the way that /usr/share/apport/package_hook attaches the log file:
        pr[mkattrname(l)] = (l,)
and
                pr[mkattrname(path)] = (path,)

will cause those files to be compressed. If you don't want that, you can use hookutils.attach_file instead, which won't compress them.

However, I think it's a bug in Launchpad that this results in the files being downloaded rather than viewed inline. It should be possible for the browser to transparently decompress them if the HTTP headers are set correctly.