Padding with black video frames does not work in MediaConvert

I have the same scenario explained in the first section of https://docs.amazonaws.cn/en_us/mediaconvert/latest/ug/video-padding.html( the first picture), the video track starts a bit after the audio track, and I am getting a video that is clipped to the duration of the video track. The beginning of the video where there are no frames is cut off. I tried the same transcoding by creating a job in Elastic Transcoder and i am getting the desired output. In the elastic transcoder it seems that the first frame of the video is copied at the beginning where there is only an audio track and after that the video starts. That job that i am creating in MediaConvert outputs a video and a thumbnail. When i select Pad:Black in video correction it says that there are no audio descriptions in the frame capture section in the output, and then i have to delete the output for the thumbnail so I can make a test with black frame padding. Even after that I am still getting a video with a clipped beginning. Any additional information will be much appreciated.