Please don't assign issues to someone when you first report them. We get e-mails for every issue in every category/project.

"Assign" in our context means that someone has agreed that they can work on the issue. A developer will assign the issue to themself when they have decided they can work on it. Otherwise it should stay not assigned until / unless someone will be working on it.

This is expected behaviour. "Thank" means to give a member some points as a thank-you for their contribution. The form for giving points exists on the member's profiles tab. I'll double-check in v11 to make sure the page jumps down to the form and, if not, I'll put a hash jump in the URL.