Matthew Turland has come across an "interesting bug" in PHP's stream wrappers functionality - some strange 404 or 500 HTTP errors in one of his scripts.

I wrote a small script a while back that's gained a surprising amount of popularity thanks to a plug from the site that it posts to. [...] I learned that this [connection from the script] could be done with streams, I attempted to implement it in that fashion, but ran into strange issues where I would get 404 or 500-level HTTP errors rather than the response I was expected.

He eventually found the bug related to his problem (in the 5.2.x branch) but happily notes that it has been corrected and will be patched in the upcoming 5.3 (and 6) branches.