Image Backup File Format Changing From RAW To Compressed VHD?

I seem to run into this once in awhile. I’m using BTRFS filesystem for my backups and have the image backup file format set to RAW. Sometimes when I check the settings, I find the format has seemingly auto changed to Compressed VHD.

What could be causing this? If I find this while images are backing up, what happens if I change it back right away?

Thanks