There is a known issue with Apache caching of non-parsed content.

For example if you post an image, then replace it on the file system, the image shown in the browser is still the original. Deleting it and then placing a new version with the same name doesn’t help either.

This happens only to non-parsed files (images in particular). Apparently Apache has a glitch with network mounted folders of NTSF format dealing with permissions (as usual), which is also true for mounted folders from VirtualBox. So to stop Apache from reading the cached version and instead read from disk just uncomment/add the following line to your apache.conf.

#Disable image serving for network mounted drive EnableSendfile off

Here’s a link to the discussion.