It is really an idea, rather than a bug as it currently is intended to make five second videos. So, I moved your post from bug to idea.
You can make longer videos now, but it takes some additional work. You can take the last frame from a generated video and use it as the keyframe for a new generation. And keep doing this for as long as you want the video to be. You can then assemble the clips into one video in a video editor.