The legal answer varies by jurisdiction; in practice, though, it's unlikely you'd be charged with unlocking your own bike (assuming it was a legal place to lock it up in the first place).
Legality aside, I'd personally also want to make sure that I wasn't about to leave someone else's bike unlocked and sitting there, waiting to be stolen. (In most cases, the owner of the other lock has just screwed up: while locking up their own bike, they accidentally managed to hook your frame/wheel/whatever as well.) One of my worries with picking someone's unknown padlock is that I'd want to be sure I'm
really familiar with it first... I wouldn't want to discover after it's open that I couldn't relock it (
e.g., if it's some cheap dimple lock that shoots its driver pins and springs into the keyway if it's rotated without a key in place).
Anyhow, none of that was really an answer to your question.

Personally, I wouldn't do it: I'd leave the other person's lock alone... and, if I really had to get my bike, I'd either call the property manager or the the local non-emergency police number first, to report what I was doing, before I removed the lock.
And now a funny, but very related story: a friend of mine was in a similar situation a few years ago. He was on his way back from a party and found his recently-stolen, heavily customized bike sitting chained up to someone else's fence. (He was sure it was his bike, because of all of the custom work he'd done on it.) So, he cut the lock, left a note and took the bike home. You can imagine his surprise when a REALLY angry guy found the note and called him, demanding his bike back. It turns out that, shortly after my friend ordered his custom bike, the shop that he'd bought all of the parts from decided that they really liked the design... and started selling that exact custom build as a stock bike in their shop.

So, he ended up having to do the "walk of shame" back to this guy's house, to return the bike, replace the lock, and apologize for becoming a bike thief himself...
So... moral of that story: if you do ever decide to remove someone else's lock, make sure it's actually your bike!
