PHP Oddity

So, I'm working on a piece of PHP software and I made a few major changes to my index.php script. Mostly just adding some include(); files to make the index script shorter and more understandable. I came across a rather odd occurrence which I thought I'd share.

One of my lines is:

$sig = "";

This is just a test variable, so at the moment I could set it to anything. When I edited the script, I must have brushed my trackpad the wrong way, because I found it turned into:

sig = "";

The really unusual thing is, when it changed to that, my script output no information. I added some words before the opening php tag, and it still wasn't outputting even them. It just returned a blank document everytime.

Does anyone here know why that would happen? Shouldn't I just get a variable telling me I used an unexpected command or something?

It's fixed, but I'm still curious. I spent most of the day ignoring my iBook because I was trying to let my subconcious come up with a solution.

-BDub