OK, that’s an awfully specific problem, but it’s pretty maddening if you run into it. In my setup I have a folder with my web app that’s on a normal Windows partition. In order to have an environment very close to our production webservers, I run a Linux VM with that Windows folder mounted within VirtualBox as a shared folder. Recently, several times, a static css or javascript file would be returning an old or cached version rather than reflecting my edits, which were done on the Windows side.

Fortunately, I found this post which led me to the description of the EnableSendfile directive for Apache. There was even a commented version of it in my httpd.conf file. As soon as I set that to

EnableSendfile off

and restarted Apache, and cleared the browser cache, all was working as I would hope. Happy day!