Can you share with me the .htaccess file, just in case?
Also, is the issue fixed if you change this line:
RewriteRule ^.*$ index.php?qa-rewrite=$0&%{QUERY_STRING} [L]
With this line:
RewriteRule ^.*$ index.php?qa-rewrite=$0&%{QUERY_STRING} [B,L]
Or maybe better, this one:
RewriteRule ^.*$ index.php?qa-rewrite=$0&%{QUERY_STRING} [BCTLS,L]
Finally, what version of Apache are you using exactly?