Yes, it changed, and on purpose.
Ever since the shortcut feature was introduced in vBulletin, many forum members have been accidentally submitting posts or new threads before they were finished typing them, by mistakenly touching the control key (or alt key under Windows) while typing.
We have removed a small convenience (using control-s or alt-s to submit a post) to avoid frustrating and embarrassing those posters, to keep the clutter of half-typed posts out of the forums, and to make less cleanup work for the moderators.
You and other posters are welcome to give us feedback about this change and about our decision that it is worth the tradeoff.