apache - Why does the web server sent the file instead of a 304 http: not modified? -

my browser send server following request:

host: www.imprimante.be user-agent: mozilla/5.0 (windows nt 6.1; wow64; rv:38.0) gecko/20100101 firefox/38.0 accept: */* accept-language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3 accept-encoding: gzip, deflate if-modified-since: fri, 29 may 2015 14:22:44 gmt if-none-match: "90-5173935ad3a1a-gzip" referer: http://www.imprimante.be/premier-avis-gratuit/ cookie: <hidden> connection: keep-alive 

the url used http://www.imprimante.be/wp-content/themes/mch_imprimante/js/theme.min.js? (note: www.imprimante.be not accessible trough wlan yet)

and server send me file (status 200) http header:

accept-ranges: bytes connection: keep-alive content-encoding: gzip content-length: 137 content-type: application/javascript date: wed, 03 jun 2015 07:18:03 gmt etag: "90-5173935ad3a1a-gzip" keep-alive: timeout=5, max=99 last-modified: fri, 29 may 2015 14:22:44 gmt server: apache/2.4.10 (debian) vary: accept-encoding 

as might notice (last-modified: fri, 29 may 2015 14:22:44 gmt) file hasn't been modified since last request.

so don't why response isn't 304 status: not modified.

i'd know why caching of files (and others) doesn't work expect it.

it bug in apache. turn off mod_deflate.