I've been noticing this for a couple of months now, but it's starting to get really annoying. After a few pokes around the support forums, I haven't seen anything similar, so am assuming it's something quirky in my installation.
Occasionally, pages (not Pages) within my WP blog trigger a download in browsers, rather than displaying content. This happens most often when posting a new entry (click "Publish", wait a few seconds, and you'll be presented with at "What should Firefox do with this file?" save dialog.
It seems to be happening more often, but frustratingly it doesn't happen consistently. It can (sometimes) happen in various parts of my blog, whether it's posting comments, publishing posts via the admin interface, moderating comments via Spam Karma 2, or even just opening the Write Post screen.
I'm stumped - if it's an Apache config issue, no PHP should execute - but the same php file will render on one request, and download on another. If it's a browser issue, it should be consistent. I've tried turning off modules, changing themes (but it happens in the admin interface, too...)
I took a screenshot of one of the dialogs.
I'd appreciate any ideas anyone might have.