When you say "I start dropping in tracks" do you mean overlay tracks - such as audio or video 2, 3, 4, etc.? One track should have no effect on transitions made on another track unless they are linked.
There are two transition modes, with the default chosen under OPTIONS | EDITING. They are "generate freeze frames" and "move clips to overlap."
Choose ASK ME and VP will prompt for which mode to use if there is not enough excess video between the two clips to be transitioned.
FREEZE will not overlap and is usually okay, depending upon content and transition type and length. This won't alter sync between the video and a non-linked audio track.
For linked tracks, overlap will shift both audio and video, to maintain sync.