Something is definitely awry. What version of Videopad is being used?
Before adding to the project, close out and restart. Prior to loading the project click OPTIONS | DISK tab and Clear Unused Cache Files.
Confirm that the video driver and Direct-X are up to date... https://www.nchsoftware.com/videopad/kb/1772.html
If dragging 'snaps back' or moves clip positions, try holding down <alt> while dragging. Or lock the tracks that you don't want altered: right-click in the area to the left of the track and LOCK TRACK.
Also try this version, which will install over the old. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest. Retain your old install file and registration info.