You have to unlock a classroom the day after term finishes to turn off a projector that a teacher left on, despite a whole-school reminder email to make sure they were turned off.
People start surreptitiously opening gates that are supposed to stay closed over the break, because they think there’s no-one around to notice.
You respond to a burglar alarm going off because some hirers were told there was no alarm in the building they hired, so when they walked in and set off the alarm they just ignored it and hoped it would turn off on its own.
You get a variety of ‘Suspicious login detected’ emails from Google Apps after students legitimately log in to their school email from Qatar and the UAE.
Co-workers who are definitely not going to hand in their notice during the holidays to screw the school over mysteriously clear their desks, by complete coincidence, despite never clearing their desks for the holiday before.
A massive Dell shipment arrives the day before you go away for 2 weeks, despite clear instructions to the reseller not to deliver until you got back.