Apache mod_alias / .htaccess, headers different on RedirectMatch vs RewriteRule

Question

Do you have any idee why the Authorization header is lost when using

RedirectMatch .*service_auth /service/

vs

RewriteEngine on RewriteRule ^(.*service_auth)$ /service/ [QSA]

With the first one I get

   'User-Agent' => 'Jakarta Commons-HttpClient/3.1',
   'Authorization' => 'Basic dGhlZHJpdmVyaXM6555udXByZQ==',
   'Host' => 'admin.mysite.uat'

and from the second

   'User-Agent' => 'Jakarta Commons-HttpClient/3.1',
   'Host' => 'admin.mysite.uat'

Thanks