[Dev-luatex] lua(jit)tex / string.format differs

Hi all, $ cat foo.lua print( string.format("%08s","1100101")) (so a one liner, nothing fancy). On my Mac: $ luatex foo.lua 01100101 on my Linux machine: $ luatex foo.lua 1100101 (where is the leading 0??) Mac: $ luatex --version This is LuaTeX, Version beta-0.79.1 (TeX Live 2014) (rev 4971) Linux: $ luatex --version This is LuajitTeX, Version beta-0.79.1 (TeX Live 2014/dev) (rev 4972) How can this difference show up? Is this something from "jit"? Thanks Patrick