Calendar.getInstance()
http://docs.oracle.com/javase/6/docs/api/java/util/Calendar.html#getInstance()
Gets a calendar using the default time zone and locale. The Calendar returned is based on the current time in the default time zone with the default locale.
What's happened is we are now in summer, so your device's time zone has changed. Every year, twice a year in many countries the time zone actually changes: https://en.wikipedia.org/wiki/Daylight_saving_time
You should probably specify a timezone in your code, and probably use UTC, which doesn't change:
Calendar.getInstance(TimeZone.getTimeZone("UTC"));