Would this article explain the behaviour you are experiencing?
Yeah, that was really helpful, thanks.
I was dragging from the remote server to the C: drive of the local machine. That article explains, then, why it was moved instead of copied. Not knowing the mechanism, I assumed dragging from the remote server to any local drive would be considered the same as dragging from one local drive to another. After I deleted the file on the local machine, I then realised it was gone from the server, but luckily I had imported it into another application and could recover it.
I think the options outlined in the article will help me sort it all out. I'll give it a try and let you know if I have any problems.
Thanks both of you for your help.