A growing number of iOS and OS X owners are reporting a glitch that displays the holidays from the wrong country in the default system calendar app. As noted by one MacRumors reader in Ireland, holidays like the pro-UK Battle of the Boyne are now showing on his iPhone calendar.
While most reports involve iOS 7.1, a few OS X owners have reported a similar problem with OS 10.9.x that also started in the past week. These users also state that the default holiday calendar now displays events from the incorrect region, with one user on Apple Support forums noting that switching the default currency back to the local designation seems to fix the issue.
Article Link: iOS and OS X Calendar Glitch Pulls Holiday Data From Wrong Countries