I layered a second audio last night, by mistake. As it wasn't what I wanted I immediately deleted it. I'm not sure of exactly how it happened but I think I opened a clip and added some audio not realizing it was a clip I had previously worked on with audio and saved. There was just one layer showing and I just popped an audio layer under it and was surprised when previewing I heard a mashup. I canceled the work so I'm not sure if the video is re-rendered losing quality when saving.