BoincTasks doesn't give the previous screen position or size.
The sorting indicators are not the same, as you closed the computer.
Next time you shutdown your computer:
Close BoincTasks using exit.
Close Windows by Start -> Shutdown. This is preferred over the Off button.
Windows has the nasty habit of not storing the entire registry or letting the program exit properly, when you hit the Off button.
The off button is fast, because most users like a fast shutdown.
So using the controlled shutdown method, you get a more complete and better shutdown of your computer.
Once the settings are properly stored in the registry you can start using the Off button again.