Just grabbed the latest ISO to test it out :) - rust9x_sample.exe sadly only works in 98/Me compatibility mode. https://i.imgur.com/nWCfTtV.png
In regular mode it seems there's a problem with the system not setting the file pointer to the end when OpenOptions::append is used: https://i.imgur.com/vvbEnWh.png https://doc.rust-lang.org/std/fs/struct.OpenOptions.html#met...