Windows 2008 R2 - large file copy uses all available memory and then tranfer rate decreases dramatically (20x)

I have a problem that was discussed in the following link but never resolved.  I'm unable to reply to that thread, so I've created a new one in the hope that someone might be able to help.

http://social.technet.microsoft.com/forums/en-us/windowsserver2008r2general/thread/74C2C9CA-F8C1-4C37-BC8C-CD074CE0C6CD?prof=required

I have two Windows 2008 R2 servers, and I'm trying to copy large (minimum 50GB) files back and forth between the servers.  If I copy a 50GB file from server 0 to server 1, the transfer rate stays at just below 1 gigabit/sec on a gigabit switch.  However, if I copy a 50GB file from server 1 to server 0, the copy begins at just below 1 gigabit/sec, but once the amount of data transferred is equal to the amount of available RAM on server 0, the transfer rate steadily decreases (will continue to decrease rapidly and might level off at just 50 megabit/sec).  It doesn't matter if the file is pushed or pulled.

Server 0 is a Dell PE2950 with 24GB of RAM and 2 dual core Xeon 5110 CPUs @ 1.6GHz

Server 1 is a Dell PE2950 with 32GB of RAM and 1 quad core Xeon E5420 CPU @ 2.5GHZ

I have seen this happen before on Windows 2008 x64 without R2, and I've used DynCache http://www.microsoft.com/downloads/en/details.aspx?FamilyID=e24ade0a-5efe-43c8-b9c3-5d0ecb2f39af&displaylang=en to resolve it.  However, DynCache is not supported on Windows 2008 R2, and it's not supposed to be needed on R2 because the problem was supposedly fixed / solved.  Interestingly, I only have the issue on one of the two R2 servers. 

In task manager on the problem server, as soon as I start the file transfer, I can watch the available memory begin to drop.  At the moment I have 24GB of RAM in the server, and about 16GB of that is available.  Once 16GB of the 50GB file has been transferred, the available memory gets down to 0 in task manager, and then the transfer rate tanks.  The OS was installed just a week or two ago.  It has Hyper-V and SNMP installed, as well as the latest Windows updates.  I then installed the File Services role as well, but the problem still exists.  Nothing else has been installed. 

Clearly there is still an issue here in Windows 2008 R2, but it doesn't seem to affect all servers in all situations.  There are also clearly other people having the same problem, but to my knowledge Microsoft has yet to acknowledge or address the issue in Windows 2008 R2.  Can anyone help?

Thanks.