This is happened twice, the same way. I go to Velsa's Villa. I approach the big door. It shows 'Open' and not 'Trespass'. Then I make my way to the door labeled 'Weaver's Storeroom' which does say 'Trespass', and enter a Trespassing area. The spiders thankfully don't give a bounty for being spotted by them.

I do my business, and leave. Back outside at the warehouse area... apparently I'm still 'trespassing' even through I left the room that I'm trespassing in. Somehow a guard (with eagle vision) manages to see me as I come out, and slaps a nearly 300g bounty on my head. This trespassing zone is HUGE, and is half the city. The only way to leave (for me) is swim in the bay. This resets the whole trespassing area.
Spoke to another player doing it. They claim the big door said 'Trespass' to them when they first entered. Yet again, it said 'Open' to me.

I doubt it would be an addon, as they aren't allowed to do anything to mess with how quests work and stuff. But something's.. strange on my end. When leaving through the big doors and turning around, then it shows 'Trespass' and not 'Open'.
I thought this was a bug at first, but now I'm not so sure. All I can ask is "has this happened to anyone else?"