Watching "Thor: the Dark World", Thor's hammer Mjolnir is called to him multiple times and at one point, it ends up chasing him around a little bit. During this, the hammer ends up avoiding a building. I thought I remember the hammer being called THROUGH objects in previous movies though. How does Mjolnir find its way back to Thor?
Mjolnir's return flight takes the path Thor deems best. The enchantment can exercise a great degree of discrimination or fly brutally back to the Thunder god, depending on his need.
In an area with innocents, Mjolnir can fly with a great deal of discrimination, touching nothing along the way Thor would deem inappropriate.
For example: When Thor was upon the SHIELD helicarrier and needed Mjolnir, it flew to him without damaging any part of the carrier. This meant it likely took a little longer than Thor would have liked but arrived in a timely enough fashion.
In an area with plenty of enemies and no allies, Mjolnir is not above hitting anything or anyone to return to Thor with alacrity. Woe be to anyone foolish enough to believe they could prevent Thor's hammer from returning to him after a throw. And yes, it will if Thor's need be great enough fly through things to get back to him. But only on the return trip of the throw.
In the old days, especially during the Silver Age, if it was able to be interrupted, it can end up sitting somewhere until he can get to IT. This was part of the story element that if Thor could be separated from his hammer for 60 seconds he would revert back to his puny human form.
In those days, Mjolnir didn't seem to possess the ability to fly to Thor because he wanted it to, or the writers used the power without a clear set of guidelines.
In the recent Infinity #4 the Avengers are forced to negotiate with an alien species called the Builders. Thor throws Mjolnir into space and it circles the Hala sun while Thor negotiates with the Builders, unarmed. When asked to kneel, Thor refuses and Mjolnir returns with an accelerated flight path and diving through the planetary atmosphere, kills the supposedly unkillable Builder...
- If you want to see this feat in all of its awesome glory, take a look at this thread on Infinity #4
Mjolnir obeys Thor’s mental commands, via his bond with the hammer, as though it was alive and, if Thor’s will is strong enough, the hammer can pass through nearly any barrier to reach his hand should he so desire. Once thrown, Mjolnir returns to Thor's grasp when he mystically calls upon it to return to him.
More on Marvel.com: http://marvel.com/universe/Thor_complete_powers#ixzz3MV9WPHNO
:D I hope that helped you