When running PHP either as a CGI or through mod_php, 
including the #! line causes it to be included in the 
output. When running as CGI this trips up the browser, when 
running through mod_php it just appears as an additional 
part of the display HTML document. 

The check is in the source code, but it's ignored. The 
patch to fix is:

*** sapi/cgi/cgi_main.c Thu Oct 18 07:01:34 2001
--- sapi/cgi/cgi_main.c.orig    Thu Oct 18 06:19:44 2001
***************
*** 699,706 ****
                        return FAILURE;
                }
                file_handle.filename = argv0;
!       }
!       if (file_handle.handle.fp && 
file_handle.handle.fp!=stdin) {
                /* #!php support */
                c = fgetc(file_handle.handle.fp);
                if (c == '#') {
--- 699,705 ----
                        return FAILURE;
                }
                file_handle.filename = argv0;
!       } else if (file_handle.handle.fp && 
file_handle.handle.fp!=stdin) 
{
                /* #!php support */
                c = fgetc(file_handle.handle.fp);
                if (c == '#') {