Today I wanted to do some calculations involving dollars and noticed the $ symbol didn't work. I also tried dollar and USD with no success, then I went to "Units > Currency" and noticed there were only a few (only the European ones, I think).
I tried a variety of things: updating currency exchange rates, closing and opening, running with HOME=/tmp... At the end it got fixed and I get all the units again, but I have no idea why, nor what happened to break it.
Some idea of what could have happened? I would report this as bug, but I don't think I'll be able to reproduce it.