OK so now I'm confused. In the project I was working in, clips that I'd resized to a round figure were reverting back to their original length when moved, and soens pointed out that this is expected behavior. I thought that was strange, because I'd never noticed it before when doing exactly the same thing. I thought I was going crazy.
So I just tried an experiment. I started a new project and inserted a MIDI track. I then dragged a Groove Monkee MIDI drum pattern into the track from the browser. It had a length of 7:944, which I resized to 8:000. Now, when I move it around, it retains its size. In fact I can make it 16:000 and it still retains its size when I move it. Sonar does not truncate it to cut off the empty space.
What is going on? Confused!