When clicking with the left mouse button, dragging files to another Nautilus
window, holding the left shift key, then releasing the left mouse button,
files are copied to the target location rather than being moved.  It is my
understanding that holding shift should force a move, control should force a
copy, and alt should force a prompt: the other two work fine, but shift
doesn't.

This occurs when dragging and dropping files or folders between two locally
mounted NFS exports.  I expect it occurs anywhere where copy is the default
action.

This bug could be similar to bug 109055, but there's not enough detail in
that report to tell.