Surface snapping causes the pivot to move to a different location away from the grouped items. The pivot can be reset by ungrouping and regrouping, but the pivot moves away from the group when the group is moved again while surface snapping is on.
1. Place 3 actors into the viewport
2. Group the 3 actors together
3. Turn on surface snapping
4. Drag the group around and release mouse
Head over to the existing Questions & Answers thread and let us know what's up.