Odin was being a **** again. He wasn't sure about Thor's commitment so he gave the power of Mjolnir to Thor but when people needed him, Thor went to help them without Mjolnir so Odin decided Thor was still worthy and took it back. It was revealed that it was Odin just using Loki to test Thor. Loki went away to sulk and everyone else had a feast for Thor's prowess. However, Thor refused to partake in the feast because he didn't like how Odin had used Loki that way.
It was in the Marvel comic magazine this spring and a special Avengers collection that I saw for sale at Walmart.