Huh. Well there you have it. I just edited the file using TextEdit, added a smiley, and, yeah, it's all good. No problem at all.
*hits head repeatedly against wall*
Ouch.
Funny. I just remembered the other time I had a problem with a file that everybody else was fine with... one of the PunPoll mod files. It had EOF tags and I never got it to work; eventually I just replaced the bit of code that had EOF tags with the equivalent using print statements in the php. Sloppy but it solved the problem.
Just a sec... *checking a faint suspicion*
Oh yeah, there's definitely something with the EOT and EOF tags that Dreamweaver has a problem with: I've recently added a photo gallery to my forum and I intended to modify the login system so it would eat the punbb cookie, but I was getting weird blank page errors whenever I tried to edit the login.php file. Things just now connected in my brain, so I checked and yeah, that login.php file uses EOT tags. It's the only thing in common between all these files... and editing files that don't have these tags doesn't cause any problems. Things are coming into focus!
I guess I'll check the Dreamweaver bug reports, since it seems to be a pretty specific problem. I guess if anyone else comes up with this problem, at least you can tell them it's probably not the pun code, but the editor's problem. Or is my logic all screwy? I'm not ready to discount that possibility yet. I still don't understand the how and why of this bug...