updated 01:22 pm EDT, Mon July 7, 2014
US, UK, and Russia apparently immune
Over the weekend, a number of iOS and OS X users have started reporting glitches with Apple's official Calendar app. Affected people will see holidays from other regions appearing on their personal calendar, such as UK holidays in Ireland, or Mexican, Canadian, and even Hong Kong holidays in Lithuania. Some countries appear to be immune to the bug, including the US, the UK, and Russia.
Apple has acknowledged the issue and is said to be working on a fix for a future version of iOS. In OS X, it may be possible to eliminate the problem by making sure the currency used is set to the local format.