Hey, at least Qik lets you save the file... Apparently iMovie doesn’t even do that! ;)
Turns out there's an issue where having too many large still images in your video can cause problems on export. Given that Qik doesn't do still images in video, and simply cropping a video in iMovie wouldn't produce the problem, there's no comparison. I'd expect a software update. Version 1.0 of any software usually has some issues.