I've never had a problem with accidentally resurrecting an old thread. Whether posting with quick reply, in the advanced mode, or quoting another member, the warning is plainly visible above the "Submit" button. Do other members experience the behavior of MobileRead on their computers differently?
Now, if someone's using Tapatalk, it would be easy to resurrect an old thread: No warnings appear. Same thing with MobileRead.mobi. But every time I go to post in an old thread on MobileRead.com, I see this, and to me at least, it's pretty hard to miss: