Right it was setup so you could only tag your own threads. I've changed so that senior members can tag any thread. Check the icon near the thread title.
Not a bug or a problem, but I don't see a suggestion thread so I hope you don't mind if I ask here. On the Juventuz Retro style, can the thread path be added to the bottom of the page? For example, on top it displays "Home > Forums > Site > Support Forum.