That's the grammar for PHP integer literals[1]:

    decimal     : [1-9][0-9]*
                | 0
    
    hexadecimal : 0[xX][0-9a-fA-F]+
    
    octal       : 0[0-7]+
    
    integer     : [+-]?decimal
                | [+-]?hexadecimal
                | [+-]?octal

"08" and "09" do not match any of these.

    php -r "var_dump(08);"

Yields "int(0)", while the case should rather be treated as a syntax error, if you ask me.

The bottom line probably is that your literals just shouldn't have leading zeroes…

[1] http://www.php.net/manual/en/language.types.integer.php