Here is a user-side fix in bookmarklet form:
Code:
javascript:(function(){var a='http://www.flyertalk.com/forum/showthread.php?goto=newpost&t=', b=$('a[href$="new-post.html"]'),i,u,t;b.each(function(h){u=b[h].href;i=u.lastIndexOf('/')+1;t=u.slice(i,i+7).replace(/[^0-9]/g,'');u=a+t;b[h].href=u ;});}())
I only tested the bookmarklet once and on only one browser, but while slogging through figuring out the required code I did complete several more tests of the old-style URL, so far without the URL failing to function as expected.
As with all bookmarklets, it has to be applied anytime the page it affects changes. Therefore, if it is not already your practice, you should Ctrl-click or shift-click all -new-post.html links.
The bookmarklet uses jQuery (already used by FT), so it will take a bit more work to convert the bookmarklet to a GreaseMonkey script than otherwise, but I'll post that when it is available.
ETA: I don't access FT threads via MyFlyerTalk, so it hasn't been tested there. It should work, but let me know if it doesn't.