This is happening because of certain video files that you have. We have identified and should be releasing a fix to resolve this slanting playback. In the meanwhile, you can follow these instructions to resolve your DVD burn issue as a workaround.
1. Open RealPlayer
2. Select the video(s) you want to burn and right click from the Library and choose Edit --> Convert
3. RealConverter will open up. Choose MP4 as your "Convert To" and click Start
Use the newly created MP4 video to burn to your DVD.
If the issue persists, please note that our next release will have this fixed. Don't have an ETA on when the next release will be but it should happen pretty soon.