Well, ctrl+z (undo) now works in all browsers. This has been a longstanding bug, but I finally traced the problem down to (of all things) the character counter.
I have no clue why the character counter was causing ctrl+z to not work in IE, Chrome, and Safari. Nonetheless, the two were conflicting. And given the choice between one or the other, I much rather have the ability to undo rather than have a character counter.
In the process of doing this, I also made some changes to the autosave feature, which is what I originally thought was causing the issue. From now on, posts will only autosave every 15 seconds rather than every time you type a character. This should help reduce some server load.
