I have set Caps Lock to work as the compose key, and I'm using the "English (Dvorak international with dead keys)" keyboard layout*. After upgrading to 13.04, I now see the same symptoms on two very different machines (custom desktop and Samsung laptop): Some time after logging in, seemingly at random and often after many hours of use, the compose key suddenly becomes permanently active for the grave accent (aka. "backtick") and typewriter apostrophe keys. Any apostrophes in this article had to be cut and pasted, since '+' produces a single acute accent (´) character and Shift-'+Shift-' produces a single diaeresis (¨) character.
What could cause this, and how do I fix it?
* By mistake (maybe I added the wrong layout or the OS reset it); I usually use the "English (Dvorak alternative international no dead keys)" layout. I'll check if this happens with the latter as well.