I am on v. 0.73

Opened a clip in the source viewer.
Played, marked in and out. Paused.
Dragged the clip to the timeline.
Clicked back to source viewer and clicked a bit further in the scrollbar to pick a different section. The in/out point suddenly jumped to where I clicked! It was totally confusing and this has to be a bug. No matter what I am doing in the source viewer, the in/out points should stay where I put them. The only reason for changing is if I put a new in point and new out point.

Not sure to understand where you clicked? In the monitor ruler? There is a feature that allows you to set in/out point by clicking in the ruler with the right mouse button... maybe that is the reason of your problem?