Group calendar view is broken in Twenty Fifteen standard theme

Just-installed wp 4.3 instance with default theme + BP plugin. See screenshot to see the trouble.
If I go in Chrome's Element inspector to view TD container for Calendar, I find "width: 10%" for class "table.calendar-view td.cal-left". If I set width value to "300px" - problem goes out. Please include something like this in your next patch.