I look at this kind of thing all the time because I work on a magazine which publishes five spreads of TV programming grids and information each month, one for each “week.” We usually run the tail-end of the last month on the first spread, and the last spread often just has a day or two, or runs extra-long. For October, the last spread, instead of featuring seven days’ worth of program schedules, it had eight.
We ended up with extra pages to re-allocated one February a couple years back. It was 28 days, began on a Sunday and ended on a Saturday. There was no way to get to five weeks! It was interesting, in a calendar-geek sort of way.
Once you consider that there are only 14 calendars (for a year) – 7 common year and 7 leap year, each starting on a different day of the week – it should be no big surprise that with the exception of Feb/29 falling on the same day of the week (which takes 28 years – as a rule) the same calendar layout will recur every 5, 6, or 11 years.
7 months a year have 31 days in them. Whenever one of these months happens to start on a Friday this happens. I wouldn’t think it’s that rare.
January of this year was the same way.