I believe offset mode is designed to be used for calibration purposes. However, a neat by-product is it gives you the ability to "offset" established settings on a track. For ex., let's say you have a track with a volume envelope on it and then decide you want to raise the overall volume of the track by 2 db. You could go in and edit every node on the track envelope to increase it by 2 db. OR you could go into offset mode and change the track offset by 2 db. In other words, the track reading would now show -8db - but the REAL setting is -6db (since you have offset it by +2 db).
There is an icon at the top of the track view window that toggles you into and out of offset mode. It a very nice feature if you have a mix you've worked on for a long time with lots of envelopes, and then realize you want to make an overall change on a track without distrubing the envelopes.
As for your pan problem, it sounds to me like you have a pan envelope on the track. That is the behavior you would get. See if there is one and delete it.