It's not a glitch. It's a feature that was previously disabled by default. I PMed Alex about it and he enabled it. So blame me if you don't like it!
It's actually a good way to help boost forum activity because people are more likely to return to threads and reply to them. - Otherwise there's a greater risk that they may forget about it even if it was previously of interest to them. For me personally, I find it very helpful because I use many forums and it helps me keep track of all the threads which I posted in. (on various different vBulletin forums)
