I was playing Oblivion, and decided to visit The Mystic Emporium. When I arrive, it's closed. The time was 12:00 p.m, I figured maybe NPCs take days off. I come back the next day, at 2:00 p.m, still closed. "Very odd", I say to myself. I wait for three days and come back, at 5:00 p.m. Still closed. so this time, even though I am a noble Paladin, I pick the lock, and take a look inside. I expected to find the owner dead, perhaps he was murdered by one of the townsfolk, I've seen it happed before. To my surprise, the owner, Halindil I believe his name is, is walking around the shop. He greets me, and continues walking. Apparently he had somehow locked himself in his own store. I waited for a few hours, and he left. I then come back the next day, and guess what, the shop is locked again. I pick the lock, and again find him wandering around. Does anyone know why Halindil is locking himself in his own store? Did he have one too many Skoomas?

What mods do you have installed?

It's from the Fighter's Stronghold plugin. You won't get in trouble for breaking in, but you can still get a bounty, so you'd better check that real quick.

According to the http://www.uesp.net/wiki/Oblivion:Mystic_Emporium#Bugs, unlocking the door to Calindil's private quarters will allow the front door to remain unlocked. You'll still only be able to do business between normal business hours though (8am to 8pm).

IIRC you can use an Open spell to unlock doors without incurring a bounty.

Yea I see that happen at times too.. I thought it came from his new Guest now staying in there and doing some selling of her-own. The woman that sells the deco for Frostcrag Spire. I always find that the door does what you say when she comes into play. Everytime I pick the lock and just have to go into that store, the owner is always behind the desk and comes walking into his standing position behind the desk to sell things. After that the door is unlocked. He usually has two customers outside the door when its locked too.

It could also be from the Rosethorn hall though like another has mentioned, but I never noticed. I usually get the Spire before I get the Hall.

I do not have the Stronghold plug in, but have had another store do the same for me.
drewbstr is completely right, I just "broke in" with an open spell all sorted quickly.
If you are on the pc you can also write in the console "unlock" to do so.

I play on the Xbox 360 mate.

I've seen this happen, too, with Soris Arenim's house in the IC Talos district. I shop up to buy the mage's staff and his door is locked. And it stays locked, permanently, for days. Finally, I pick the lock and enter, and his wife runs up and says, "You shouldn't be in here!" Then I buy the staff from him and the game goes on.

Not sure why it does it, tho ...

~ Dani ~

On my first character this happened to me. It very frustrating cause that's my favorite store to visit! Anyways, I just gave up and every time I go I just pick the lock. Gotta love that skeleton Key!