Hi Stuart,
I just checked at my end, it looks proper(3rd August is a Sunday). As calenders are quite straight forward, I can only think of two things.
1. Check the date on the BO server and the web server, make sure it is correct ( Very less possibility)
2. This is a bug as I checked it on BI 4.1 SP03 and you have mentioned that you are on BI 4.0
Regards
Chinmaya