error in Projects.Timesheet?

Can you explain to me why the sum of the hours for the month is wrong? (please see the attachment)

(if the attachment is not there, you can see the screen capture here: http://mazzaroth.ca/tmp/SafariScreenSnapz001.jpg )

I am expecting to see 21.00 and I see 21.40... Where does this 0.4 comes from?

Thanks