hahah.. i tried that; but IB shows correctly that the order wont be sent to exchange till open on sunday. So you cant actually buy or sell them; which is good.
I've noticed it also. Every weekend, the futures price shows the Thursday close. It's been like this for a while now.
Going right now, Saturday Jan 21st 2017 10am..60.50 x 60.75 on the ES, looks like Thursdays clsing data. Eur and Cad going too..