Problem #1: Since the "from child" filehandle is non-blocking, the parent could read from the pipe faster than it fills up, causing @files to contain only a partial list. Since the data is coming from the internet, that's actually quite possible. Why did you make it unblockable anyway? Just exit the loop when sftp> is encountered.

Problem #2: You don't empty the pipe attached to sftp's STDOUT once you've done reading file names, so it could fill up and cause sftp to block.