I addressed this to Corel support but they are not sure whether it is a fault or a feature 

 When I add a time freeze segment to a clip there are also time freeze segments (red areas) added at the beginning and the end of the clip. That's of course not what I want because it especially gives problems with transitions. See here https://youtu.be/zcuL4-gh_K4 (the screen recording only shows how a time freeze is erroneously added at the beginning but there is also an unwanted time freeze added at the end of the clip.)

Take a video, trim it at the beginning and at the end, insert a time freeze halfway. Then you will see that the beginning and end of the clip have been replaced by stills.