The tack/pin is only used to pin a section open, it does not pin a closure. You have to take into consideration the overall state of the section based on the + and - buttons on the left-hand side as well.
Here's how it applies.

• If the tack pin is turned off (no pinning) then it will be open or closed based on the last setting of the + and - and whether when you move away it is already open or closed. It will remember that even after logout.
• If the tack pin is enabled then it will always force the section open. So if you set the pin, close it down with the - button on the left, then navigate away and back again it will override the last close to open it again. Again, even a logout and log back in will remember to pin it open again.