Perhaps calling next part is consuming reader, so when you break at once you hit io.EOF, the reader you memorised has been consumed.
Again, just a guess, I’ve never used the multipart package in anger. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.