After a private message has been sent the redirect is incorrect. It seems to be a cookie that is set with a redirect url that is different than the page before the new (or reply/forward) message page.
The most common one that comes up when writing long messages is: /client/keepAlive
But, if replay is open in other tabs and I navigate the site in those tabs before sending the message then the last page I viewed becomes the redirect url.
A few friends have this issue as well.