Incorrect line number in compiler error

[emil14]

import { fmt }

def Concat(prefix string, suffix string) (res string) {
    (:prefix + :suffix) -> :res
}

def Main(start any) (stop any) {
    fmt.Println
    concat Concat
    ---
    :start -> ['Hello, ', 'World!'] -> [concat:prefix, concat:suffix]
    concat -> println -> :stop
}

when i try to do neva run the compiler says :0:0: multiple senders are only allowed at the start of a connection

presumably the 2^32 is wrapping around to 0