Apparently, this has happened to multiple people and HB just helped me solve this and should be documented. When I made long PMs or long posts to categories (such as posting stories, etc), when the scroll bar appeared due to the length of the message being composed, I started losing control of my editing. I couldn't highlight properly, the cursor was unstable, I couldn't see text I was typing because the scroll bar wouldn't raise it in to the viewing area of the message box, etc. Basically, I had to edit elsewhere and copy and paste into the message box for long messages. I use Internet Explorer 8 and Windows 7. HB said he has no problem with Firefox but certainly did with Internet Explorer. He had me try this and it seems to have worked and still is working. So if anyone has the problem with jittery/jumping message boxes:
1) uninstall Abobe Flash Player which is used by this forum
2) reset IE settings to default
3) reboot your computer
4) reinstall Abode Flash Player
Problem solved!!! Go down to 4th post in this thread....that is the real answer I've found