<p>Right now we've got web pages that show UI elements, and web pages that just process form submissions, and then redirect back to the UI pages.  They do this using PHP's header() function:</p>

<pre><code>header("Location: /other_page.php");
</code></pre>

<p>This causes a 302 Found response to be sent; according to the HTTP 1.1 spec, 302 is for cases where "The requested resource resides temporarily under a different URI." <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.3" rel="nofollow noreferrer">[HTTP 1.1 spec]</a></p>

<p>Functionally, this is fine, but it doens't seem like this is the proper status code for what we're doing.  It looks like 303 ("See Other") is the appropriate status here, so I'm wondering if there's any reason not to use it.  We'd have to be more explicit in our use of header(), since we'd have to specify that status line rather than just a Location: field.  Thoughts?</p>

I've never used it myself... as it says in your link:
Note: Many pre-HTTP/1.1 user agents do
  not understand the 303
        status. When interoperability with such clients is a concern, the
        302 status code may be used instead, since most user agents react
        to a 302 response as described here for 303.
This seems a good enough reason to me to stick with 302.
FYI
header()
takes extra parameters in which you can set the status code:
```
header('Location: /foo.php', true, 303);
```