Is it a bug that it does not work when I click that button on my own posts? I want to lock a post I've made.

Only Staff and Moderators can use it. If you want something locked you have ping the Mini-Mod for that forum to lock it. Mini-mods only have permission in their specific forums.

sorry to hijack the thread, but why is that button visible to us? is it a glitch?

Not a coder, but I am also pretty sure for the forums groups that utilize making private forums it is so they can moderate those private forums. I am not a mod on any of the private forums to test, but I see locked stuff so I assume they can use it.

Just the lock and the checkmark/subscribe buttons. AFAIK, the lock button has always been there and has never worked on the users’ end :P

It looks like something we should be able to use but we can't

Yeah, that's why I asked in the first place - it's weird to display a button that we can't use unless we are hired for a paid position at Subeta.

I think it worked for me, I locked my own thread here. But I tried locking another one now and it didn't seem to work. So it's either stopped working, or it never worked and I was confused!