I've noticed the behavior too, but after waiting for a little bit, the price reverts to its original.

So, I'm also in the camp that the earlier search caused the last seats in the bucket to be pulled (which is actually a good thing, if you think about it -- once you click on a fare, you want those seats reserved for you so that the fare doesn't go up while you are completing the transaction). Once the earlier search times out, the seats are released back into inventory.