Comment 13 for bug 574693

Confirmed. This problem also occurs when transferring the contents of a single directory with multiple files of any size. I have also experienced it when moving a single file (I had tried tar.gz-ing the directory that was having problems). At this point, I would say that this probably has no relationship to the type, quantity, or size of the files being transferred because I have reproduced the problems under more or less every combination I can think of. While it does appear to be somewhat random, it also appears to happen more often than not when transferring data.

I can also confirm that this happens when providing a specific IP address over a local network as well as when using DNS. My FTP server, for what it's worth, is using the default port, 21.