I remember this issue years ago. Basically, the libc read()/write() functions didn't loop until they finished reading the number of bytes specified. While that behavior may technically meet POSIX standards, it isn't standard behavior. Incomplete reads and writes normally only happen with special files, e.g. pipes and sockets. I don't remember what changes were merged, but it sounds like the solution was only partial. There should be a closed GitHub issue about this.