If you’ve got a limited hat that you pin to your profile and then sell/trade it you will be stuck with that item pinned and unable to remove it from your profile.
I’m pretty sure this would happen to everyone as it disables your pin permissions once you don’t own the item.
I’d suggest removing any pinned items once you don’t have them.
Keep in mind, some people have used this pin system a little differently as the people would use the pin system to show types of hats they have gotten over time and/or even traded, but they still want people to know that they had it. (Just a different perspective since you included that it should automatically remove the pins as soon as you lose it)
I agree that it should allow you to unpin a pinned item though, as it is annoying if you traded it.
Some people abused a bug where you could pin anything so your ‘show off items you had’ thing I would say is made pointless.
I do not disagree, I just wanted to give you a different perspective on it on what some people were doing. Myself, I just show off some of the hats I traded away that I was proud of achieving like the Clockwork headphones, Sparkletime fedoras, etc… that i’m not in possession of still. I do use it though to highlight hats that I still have like the Boss White Hat or REM16 hat