setting header cache-control to no-store for aggregated css

I am using core CSS aggregator. The site is having static pages only. There are two aggregated CSS generated for each cache clear.
Out of which first css is always having a header cache-control setting to no-store, private while other is setting to provided max-age.
The .htaccess file is already having below code snipped from core but not working correctly for first css file only. Due to this issue while loading the css, there is unnecessary hit to drupal server, causing performance issue.

<IfModule mod_expires.c>
  # Enable expirations.
  ExpiresActive On

  # Cache all files for 1 year after access.
  ExpiresDefault "access plus 1 year"<FilesMatch \.php$>
    # Do not allow PHP scripts to be cached unless they explicitly send cache
    # headers themselves. Otherwise all scripts would have to overwrite the
    # headers set by mod_expires if they want another caching behavior. This may
    # fail if an error occurs early in the bootstrap process, and it may cause
    # problems if a non-Drupal PHP file is installed in a subdirectory.
    ExpiresActive Off
  </FilesMatch>
</IfModule>