Are you sure you selected restore from Master Public Key?
Are you running the latest version?
No, I did it using the "deseed" command line option. BUT I have just tried it using the 'restore from mpk' way and it has the same result: I can still see the private keys. I'm using version 1.9 which I believe is the latest?
ETA: could someone just check if their electrum does the same thing? ie. use a seedless wallet, go to the receiving tab, right-click an address. Is there a menu option there to display the private key? Does it in fact do so? Can you verify that is the right private key for that address? For me it's 'yes' to all three questions. Am I right in thinking that this would be a serious flaw if it's replicated?