During subscription extending the next month wasn't calculated properly recently

Consider this:
$thisMonth = date("m");
$nextMonth = date("m",strtotime("+1 months"));

The first line of code will output the current month in the format 0n. The second line results in the current month added with 1.
This means that an update on 31-01-2013 will result in a $nextMonth of 03 - because February only counts 28 days. Good news for customers who don't feel like paying for February!
The proper way to calculate the next month is by creating a DateTime object and 1) first determine the next month based on the current date and 2) set the day to the first day of the previously calculated month. After that, display only the month of this new date:

$currentDate = new \DateTime('now');
$currentDate->modify('first day of +1 month');
$nextMonth = $currentDate->format('m');

And finally we will have the right 'next month'.