It isn't a bug, btw, it's just part of the forum's design.

Anywayz, yes, you're right, you have to ask an admin or mod to delete your thread.

Yeah, the forum does not have any thread deletion available for users, even if it's their own threads. This is because, from experience, that when a problem occurs... it was very hard for anyone to do much with lack of proof. Because what's completely deleted cannot be retrieved back at all.
One can delete thread or post by just reporting that thread or post using the exclamation mark icon located below each post (also known as the Report button).

I see. ok thank you for the answer. I ll just report it by clicking the exclamation mark icon!