Hmm - I wonder if the system's confused about that.
If you inspect the volume under Windows, are there any files/folders called:
Network Trash Folder
... or similar present (like a load of files called ._something.ext)
I'm wondering whether deleting (via the Windows machine) any existing Mac-related meta-data on the disk might help. This is purely a shot in the dark, mind you.
I only have one SMB-mountable device here (internal disk on an ancient Win98 laptop) and can't test whether moving that to a USB-connected local device causes problems for me.
Another thought - anything in /var/log/system.log relating to failed mounts of the USB disk? You can get to all these logfiles via the Console app.