Thanks, rj. And an especially big thanks to Don Chambers for helping me out with this one. Don took a tester I made and ran it on a server using PHP 4.3.11.
Turns out it's not PHP at all. The problem is that some FTP clients are incorrectly mangling the file during the ASCII transfer. This file has Mac-style linefeeds; the FTP server is supposed to convert them to its local linefeed style. Instead, it's removing the linefeeds altogether. That's not cool!
You can try out the tester, too; just download
http://judebert.com/progress/media/s9y/sumcheck.zip to your local machine, unzip it, and put the files in a single directory on your web server.
It's important that you upload the four files correctly. The sumcheck.php and screen.ascii.css should be uploaded in ASCII mode. The screen.bin should be uploaded in BINARY mode. The screen.css should be uploaded in whatever mode your FTP client thinks best. The files are named so that your FTP client should pick the correct mode for each.
Then just visit sumcheck.php, and you'll get a nice XHTML compliant webpage explaining everything.
Here's an example.
The Solution (impatient people skip to here)
Hoo boy, was that file ever hosed; I'm surprised it ever worked. Garvin already did the right thing by fixing the file. You can download the next nightly build and be happy.
Sorry for the inconvenience, and thanks for helping us find and fix this problem!