I can tell you the Timeline has a lot more housekeeping to go through than the Viewer does. The Timeline has to keep track of whether or not you're playing out to a tape machine and change the sound sync accordingly.
But that doesn't give you a second or two offset. Are you sure it's a full second. Can you count "One Potato" between the sound and the action?
Go down to View, External Video, and make sure it's off, but I don't think that's what's wrong.
<<< others clips have no problem.>>>
Other clips shot with that exact same camera on the same day?
Koz