It seems the Project Statistics only update after a save, or similar. If I type a few words and check Project Statistics, I get an outdated figure. If I save, and check again, the figures are updated.
This is not a bug - just the result of the fact that for speed reasons, the project statistics use saved data rather than live data. This is because of the number of files it has to deal with.
Perhaps opening the statistics window could force a save?