Page not found - %20 in url

Hi all,

So I'm stumped with this problem and hope someone can help. CI v3.0 is installed in a subdirectory 'api'. 

When I am accessing this URL via CI I get a 404 error - 

Code:

https://someurl.com/api/session_controller/login_redirect/User%20Name/jjfdsiien32

The error in the logs is:
ERROR - 2015-11-16 17:02:52 --> 404 Page Not Found: Api/session_controller

See that Capital A in Api? That's weird right? 

However - this URL works ok:

Code:

https://someurl.com/api/session_controller/login_redirect/UserName/jjfdsiien32

There seems to be an issue that the directory name(!) is getting ucfirst'd when the URL contains the %20 character. 

Here is our .htaccess file (in api dir) - 

Code:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /api/index.php/$1 [L]

Any help on fixing this one would be great. 

Cheers,
Gareth