[TYPO3-ttnews] Days of month wrong in Newscalendar month view

[Tony Lush]

We upgraded a site from tt_news 3.0.1 to 3.1.0, and TYPO3 from 4.3.x to 
4.5.9. Newscalendar stayed at its most recent 2.1.5.

Now the month view shows the first of January, 2012 under the Saturday 
heading, instead of Sunday as it should be. The individual items show 
the correct date, time and day of the week.

Is there a logical reason why this should be?

Regards -- Tony