If you simply write 08 and 09 (without quotes) or any other numeric with a leading 0, PHP believes you're writing an octal value, and 08 and 09 are invalid octal numbers.
http://www.php.net/manual/en/language.types.integer.php
Syntax
Integers can be specified in decimal (base 10), hexadecimal (base 16),
octal (base 8) or binary (base 2) notation, optionally preceded by a
sign (- or +).
Binary integer literals are available since PHP 5.4.0.
To use octal notation, precede the number with a 0 (zero). To use
hexadecimal notation precede the number with 0x. To use binary
notation precede the number with 0b.
[...]
Warning:
Prior to PHP 7, if an invalid digit was given in an octal integer (i.e. 8 or 9), the rest of the number was ignored. Since PHP 7, a parse error is emitted.
