It works properly with my test case. What is the rewrite rule to redirect /a/info.php to /b/info.php? I wonder if the request got redirected at all.
My rewrite rule in /a/.htaccess
Code:
RewriteEngine on
RewriteRule phpinfo.php /2/phpinfo.php
It performs an internal redirect which does not change the URL in browser, if external redirect is prefered, just add "[R]" to the end of the rewrite rule, same result.