Video and audio: 2 stop playing when user clicks away and 2 re-set themselves automatically, all without triggers.

I am using my local drive (no USB) to create a SL project using the content library for 4 videos. I have added audio files to each video. Each video replays until the audio is complete. All videos have a 'Play' button with a trigger to start video/audio and to hide the 'Play' button once the user clicks this. On 2 of the videos, when the user clicks 'Play' and exits the video before it has finished the video/audio and 'Play' button reset themselves without a trigger, so the user can play it again (this is handy, though I'm not sure why SL does this without a trigger). On the remaining 2 videos they stop when the user clicks away before the video has finished and there is no option to press 'Play' again once this happens. Is this a bug or something I am or not doing?