Well its my first time that I see that, too.
Looking at the MEL and the flysmart what I understand is this:
Since one wing A/I valve is open, anti icing will be available if you need it by pressing the wing a/i pb. The penalty for a takeoff or G/A would be calculated and its the same when you select wing anti ice on, on the flysmart.
What is not written is that since one side will be on contniously, if you encounter icing buildup you will be flying with assymetric wing which is very dangerous. So I would put the thing on when in doubt about icing