I love DOpus but something I regularly have a problem with is that it keeps movie files locked forever after you've clicked on them once, meaning you can't rename or delete them without killing the DOpus process. It doesn't matter whether you have auto-play off or not, or whether you go to a different file/folder, having clicked on a video once locks it for good it seems.
I always have the preview panel enabled (I'm a game developer, I look at a lot of textures / models / screenshots / video captures) and so having to remember to turn off the preview panel before clicking on a movie is a pain.
I've seen some other threads on this advising turning off the preview pane but that's not really a solution. Not releasing a file lock when you're no longer previewing seems like a bug to me?