You used an tag without a date context

Back when I ran MT 3.3, I implanted calendars on all my archive templates. To have the month associated with a particular archive to appear, I used the MTCalendar month="this" option.

However, ever since I upgraded to MT4, I receive this error when rebuilding my templates:

"You used an tag without a date context"

I understand this error only crops up when MT cannot find a timestamp to lock onto. Has the behaviour changed for MTCalendar between 3.2 and 4.1?