Apache Header Module Loaded but can’t set headers in htaccess

I have Apache 2.2.29 (unix) setup and running on my new dev machine (mac). I am trying to set CORS headers for an API project – something that I have done many times.

The htaccess file for the project looks like this:

<IfModule mod_headers.c>
    Header set Access-Control-Allow-Origin "*"
    Header set Access-Control-Allow-Methods "POST, GET, PUT, OPTIONS, PATCH, DELETE" 
    Header set Access-Control-Allow-Headers "X-Accept-Charset,X-Accept,Content-Type"
    ServerSignature Off
</IfModule>
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteBase /cms/public
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_URI} !^/(favicon\.ico|apple-touch-icon.*\.png)$ [NC]
    RewriteRule (.+) index.php?p=$1 [QSA,L]
</IfModule>

and the headers module is loaded in my conf:

LoadModule headers_module libexec/mod_headers.so

The module file exisits in the location shown in the apache conf and is it loaded OK:

dan$ httpd -M

Loaded Modules:
 core_module (static)
 mpm_event_module (static)
 http_module (static)
 so_module (static)
 authn_file_module (shared)
 authn_dbm_module (shared)
 authn_anon_module (shared)
 ...
 headers_module (shared)

I have also checked the conf override settings in my main conf and the included vhosts conf:

<Directory "/Users/dan/Sites">
    Options Indexes FollowSymLinks MultiViews
    AllowOverride All
    <IfModule mod_authz_core.c>
        Require all granted
    </IfModule>
    <IfModule !mod_authz_core.c>
        Order allow,deny
        Allow from all
    </IfModule>
</Directory>

However, headers aren't being set as expected. Heres the response headers when making a request to an API project using the above htaccess file:

HTTP/1.1 200 OK
Date: Wed, 22 Jul 2015 10:36:05 GMT
Server: Apache/2.2.29 (Unix) DAV/2 mod_fastcgi/2.4.6 mod_ssl/2.2.29 OpenSSL/1.0.2c
Expires: Wed, 15 Jul 2015 10:36:05 GMT
Pragma: no-cache
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: application/json; charset=utf-8

I have tested the application setup in other apache environments and it is working as expected…so it's definitely something to do with my setup. It's driving me crazy!

Any thoughts?
Dan