Sound Issue in Replays With Pyke Ultimate

I frequently make montages of in-game moments using the replay & highlights system. Today I discovered an issue. I was playing and managed to score a nice triple. I went into the replay system to record and save the moment. Everything seems good. Then, going back into the save file, I discovered that as I cast his Ultimate, all sound in the save file cuts out abruptly. If I watch the moment in the client's replay, the sound is fine. But when I watch the saved webm file, there's no sound right when the ultimate goes off. Same thing happens when I convert the file to an mp4 file for Windows Movie Maker. Is it possible to fix this, or will I just have to live without the menacing sound of the kills?