In case y’all wanted to know about it, I’ve seen this problem twice now when attempting to post using the quick reply box:
I’m logged in, reading threads and I see one I want to respond to, so I take my time and compose a masterpiece of a post in the quick reply box, then I hit submit and I’m prompted with the login screen. After the login screen, I get an error saying something to the effect that I’m trying to access an invalid thread ID. If I hit back, I can get back to the quick reply box, but my thoughtfully-crafted post is gone forever, so I’m forced to replace it with something idiotic (as I don’t have the energy to make another masterpiece). Note that this time, submitting the quick reply box actually submits my post.
And that’s my excuse for not having more brilliant posts.