Oh yes. The ISO definition is pretty straightforward: «The first week of a year is the week that contains the first Thursday of the year.» (http://en.wikipedia.org/wiki/ISO_week_date)

Actual implementations often look more like this: http://www.epoch-calendar.com/support/getting_iso_week.html

Implementing it as a one-liner would be an interesting code golf exercise.

Could you elaborate what exactly is the bug there?

So that seems like they're doing some kind of math using the week of year in the calculation- but for what purpose? The UI doesn't seem to give you any options for day of week, just time of day.

Maybe there's code in there that checks day of week but it's hardcoded to run every day to make the UI simpler.