hi9, you're right, from a purist point of view, but gender throws a bit of a wrench in the gears. I argue that the traditional 'default to masculine' rule actually places women in a place of distinction, that "he" can be male or gender-neutral, but "she" is always female...but for some reason, women don't really buy that pitch.
It looks sloppy to me, but I think there's an argument to be made that, in 21st-century English, the gender-neutral pronoun "they" can be plural or singular.
Better English: should be "until everyone does his tasks," not "their tasks" ("everyone" is a singular noun, which is why saying 'Everyone are sad' sounds off--'are' goes with a plural noun; so instead, 'everyone is sad,' which would be sad, is correct.) Sorry to be the grammar Nazi, but this kind of thing annoys me nonetheless ;)