I just discovered a problem using V6.24 and V6.28 beta of videopad concerning the video cache of the sequence preview (export works well).
Example: Drag any mp4 video clip A to video track 1 of the timeline. Now drag another mp4 video clip B to video track 2 of the timeline, "on top" of video A (video B must be shorter than video A). Preview the video - everything is ok. Now click at the end marker of video B and drag it to the left, make it a little bit shorter. Start the preview again - it's exactly the same as before, the cache probably doesn't update and therefore still shows the whole clip B.
Note: If you change the preview frame rate in the options or if you move video B from video track 2 to video track 3, the cache seems to update. After that, the preview is correct.