I've had this problem intermittently for a while. It seems to occur after the endless Ubuntu updates, then I fix it. Then it comes back again. Recently it effected several characters, now (as of last restart) it's only uppercase P from the 'Ubuntu' font that is effected.
Any ideas on solutions?
Bonus points for identifying the cause!
I've tried the standard
sudo fc-cache -fv but no luck this time.
I'm on Ubuntu 10.10