Back Cover Image Type not set for MP4

Working on ver 3.07, adding/having multiple images to mp4 files via the extended tag editor. it seems that no matter what i am doing, the images' type is being set only for the first image.
I tried using the extended tag menu as well as right click on the main image preview screens, in both cases i get a menu to pick the image type from. something is being done once approved, however, when flipping between the images, the type is lost for all images other than the first one

see here:

Hi. It is MP4 and it shows only front cover and other
Not able to set back cover type

Yes, exactly. That's the way that mp4s behave according to standard - so -> no bug. Or one that you have to clearify with the authorities that make that standard.