Looks like the files are missing the no-cache meta directives. I'll add them in.

A quick-and-dirty fix is to add some comments to jpgraph.php (see below), although this will require the graphs to be re-downloaded every time. More investigation needed...

function Headers() {
    //if ($this->expired) {
        header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
        header("Last-Modified: " . gmdate("D, d M Y H:i:s") . "GMT");
        header("Cache-Control: no-cache, must-revalidate");
        header("Pragma: no-cache");
    //}
    header("Content-type: image/$this->img_format");
}

Is this still an issue?

Don't know if this is an issue in 0.17.x.

I'm still on 0.15.4...

Still an issue in 0.18.a4:
after changing the project you have to refresh the page to get new graphs.

Reminder sent to kraades

niet vergeten.

Thank you for taking the time to report a problem with mantis.

Since this problem report was originally made, a number of releases have occured.
It appears that this issue has either been fixed, or may not be a relevant report for the current release.

Unfortunately you are not using the latest version (version 0.19.2 )
and the problem might already be fixed. Please download the latest release from http://www.mantisbt.org/download.php

If you are able to reproduce this bug in the current release, or have some more information on how this feature could be improved in the current release. Please either change the mantis version on this bug report
to the version you tested and change the status back to "Open", or open a new issue report wit more information.

Again, thank you for your continued support and report.