“0” preceded IP Addr converted to octal

Most IP stacks are converting IP addreses with preceding zeros to octal numbers instead of decimal.
e.g.
>ping 10.10.10.010
will ping to 10.10.10.8 (because 010 is translated to octal representation).
Does anyone know WHY does all IP stacks perform this conversion?
Is it backed by a standard?
Which ?
This phenomenom is observed in ping / telnet and other IP apps, in Windows / Unix / VxWorks etc…