Transfers 'freezing' between files during site to site transfers

[SHiNGEN]

My session seems to hang and idle until disconnected when doing site to site transfers. It happens in between files in the queue, not during the transfer.

Here is a log dump of what goes on before the problem:

[15:07:12] TYPE I
[15:07:12] PASV
[15:07:12] 227 Entering Passive Mode (xxx,xxx,xxx,xxx,xxx,xxx)
[15:07:12] PORT xxx,xxx,xxx,xxx,xxx,xxx
[15:07:12] STOR TESTFILE
[15:07:13] 150 Opening BINARY data connection for TESTFILE
[15:07:13] RETR TESTFILE
[15:07:13] 150 Opening BINARY mode data connection for TESTFILE (10000000 bytes).
[15:11:35] 226 Transfer finished successfully. Data connection closed.

It hangs here. It seems like the site that is sending the data (green) never gets the message that blue is done with the file.

Not sure what could be the cause, currently using 1.4.2.831 on Win2k, going through SMC barricade dsl router. Had the same problems on previous versions too, finally decided to post something about it