Seems odd. Have you tried the machine in other sockets upstairs with the same result? If you have and the same thing happens, it must be that your upstairs sockets are RCD protected but the downstairs ones are not.
Either way, if the Dyson is tripping the RCD then there is a fault on it and it needs sending for a checkup.
Sorry i couldn't be more of a help.
Darren
September 2007