Whenever I publish or save a blog entry, I'm being prompted to save post.php instead of having it actually bring me back to the (empty) blog-entry window with the I've-posted-your-entry message. (The composed entry sticks around.)
It is, however, actually creating the entry.
When I open the post.php that's offered up in a text editor, it appears to be a 0-length file.
I haven't modded the core WP code, and certainly not anything that would interfere with the content-type HTML header as I'm guessing is happening now.