I have code like this:
$tmpPage = preg_replace( "/(<header\s*?>)/", "<header 
level=\"1\">", $tmpPage );

Ok, I want to comment this code out like:
//$tmpPage = preg_replace( "/(<header\s*?>)/", "<header 
level=\"1\">", $tmpPage );

this makes php angry. It'e reproducable, just paste the 
line above in your script and strange things will happen.

PS: The code works without the comment, so the code is 
valid.