This has often been remarked upon. People have contributed to a thread then checked the "Active" list, but their thread was not at the top, however, other threads where the latest post was older, had made it to the top of the list. It all seems quite arbitrary until, as DaisyAnn asks, you start to notice which threads are given priority and which ones drop unaccountably off the list. GNHQ of course denies this.
GNHQ couldn't understand the problem when it was first pointed out, then when it was spelt out to them so that someone there finally understood, we were told that they were "working on it".