Reproduce:
Select Connect to Server from main menu, and enter address of a shared Windows folder (i.e. smb://foo.example.org). Open mapped connection and select a folder containing a large number of files. Copy this folder to a local folder on your computer.

On my system, the copy operation will freeze after a variable time. The exact time elapsed or the number of files copied successfully varies. The copy operation will sometimes succeed, i.e. the outcome of the copying is indeterminate forcing one to always check folder/file counts and size after a copy operation.

When the operation freezes, the pop-up window displaying progress bar freezes too. If I click the Stop icon, nothing happens. Files are not copied during the freeze. The freeze never ends (i.e. I let it run for hours and it did not recover).

This does not happen when copying files/folders between local destinations, or over ssh connections.

This error did not occur in Nautilus 2.x. It appeared the moment I upgraded to 3.x, suggesting the fault is not on the server side.

Setup:
Files 3.6.3
Gnome 3.6
Ubuntu 12.10
Copying from a Windows XP Pro machine