I've been working with svn and beta builds of WordPress 2.5 for a few weeks and now that it's final I have an issue.
Part of the admin revamp is an all new interface for uploading images and other media. In browsers that support the feature (Firefox and Safari) a Flash-based multi-file uploader is used. In browsers that don't support the Flash uploader fully (Opera and Internet Explorer), a one-file-at-a-time HTML uploader is used. The HTML uploader works perfectly, but the Flash uploader does not.
The multi-file uploading capability introduced in recent versions of Flash contains a bug that sends a malformed header to the server. Because of that header, Apache's mod_security rejects the upload out of hand with a 406 error. Following the troubleshooting advice of one of the WordPress developers, I've temporarily disabled mod_security by adding to my .htaccess
>SecFilterEngine Off
SecFilterScanPOST Off
and this changes the problem but does not resolve it. Instead of a 406 error, the upload fails with a 403 error.
In the testing surrounding this issue, the WP dev team eventually added to the default .htaccess rules
><IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>
and this resolves the issue for most people, but not for me. Uploading images with Internet Explorer and Opera works fine because WordPress falls back to serving the HTML uploader to those browsers, but it always fails when WordPress serves the Flash uploader to Firefox and Safari.
Through many e-mails with the developer who built the uploader (not the Flash applet itself, but all the parts of WordPress that use it), I've begun to suspect that this is a server configuration issue, that there's something about how TCH configures their machines that may be exacerbating the problem. All the potential fixes that I've seen fail to do anything for me.
Does anyone have an idea on what might be the problem? Failing that, can anyone else confirm or refute this behavior on their own sites? (I'm hosted on grievous.)