Steps to reproduce

• Create a media (new contenttype, with a videdo fieldtype) object and insert one mp4 video (Video1.mp4)- When inserting the video, one can see that the preview is ok and the video plays correctly
• Publish the video. Once again, the preview is ok and the play is correct as well
• Edit the object and replace the video (Video2.mp4). Here we can see that the video name is updated, but the video preview is still from the first video (Video1)
• Publish the video. Once again, the name is updated, but the presented video is the first one, Video1.mp4

This seems to be a browser cache problem, because if we clear the caches, the video is rightly displayed.