I have also had this happen several times and can confirm having tried all the options including rebooting and unplugging cables, going and making coffee, and then coming back only to find that my name is still on the table I was playing at after 15 minutes.
I am not an IT guru like clyde but I asked my IT guy here and he said the same thing. Automatic updates have probably led some clients to have these problems.
I don't know much about Java myself, but the advice was along the lines of perhaps the server Java thingy needs updating to bring it in line with the latest client Java thingy?
