If you're using Internet Explorer and are unable to post long messages (when the scrollbar activates, it snaps you back to the top of the window, or 'jumps'), you need to enable comparability mode to use the site.
To do this, click the compatibility mode icon next to the refresh icon (looks like a page torn in half) or go to the Page menu and click "Compatibility View."
Of course, not using Internet Explorer and instead using Firefox (//http://www.getfirefox.com), Chrome (//http://www.google.com/chrome) or Opera (//http://www.opera.com) is the surest way to fix this problem.
If this doesn't fix your issue, please reply here and let me know.
Thanks.