Bug - calendar "hide weekend" hid Friday & Saturday

On a dashboard, in the calendar widget, clicking “hide weekends” showed Sunday-Thursday instead of the expected Monday-Friday.
I changed our admin settings to have the week start on Monday instead of Sunday and that seemed to fix the problem, but we shouldn’t have had to do that, since it will affect other places in our workspace where we might want the week to start on Sunday.

Welcome to the world where we have different weekends. If you specify a weeks starts on a Sunday, that Sunday can never be part of the week’s end (as it is defined as start). To me it is very logical that the weekend is Fri-Sat when you specify the weeks start on Sun. Is the week start set to Sun by default?