Yup - I was contracted to three months at my last place and they wanted me to stay so made me work every bit of it whilst trying to change my mind (after giving my new employer duff reference - but that's another story).
After a month they moved me from System Admin to maintenance and made me complete my notice period. Painting, driving, moving furniture...
If you're still doing your job then just keep quiet, don't burn bridges etc
'The great fallacy is that the game is first and last about winning. It's nothing of the kind. The game is about glory. It's about doing things in style, with a flourish, about going out and beating the other lot, not waiting for them to die of boredom.'