Hi,
ther's nothing strange in .htaccess file.
On my local system REDIRECT_URL works fine even with SOBI2. I don't know why this not happens on your live site. Should be veirified that $_SERVER['REDIRECT_URL'] is not empty, but I can't do it for you on a production site.
Last thing, I really don't like the way SOBI2 works. It alters server variables as it needs, ancd this can cause many problems with other components (as in our case). To work with Tag Meta, as example, if you are not able to understand why REDIRECT_URL is not set, you should understand how SOBI2 changes the REQUEST_URI (or uninstall Tag Meta) and use these, but I think this is crazy.
If you still need help let me know (be advised we should work on production site).
Regards,
Luigi