When you select a skin from a custom imported skin pack or just a custom imported skin, it uses the texture of the left leg (if looking at the character from the front) and pastes it also to the right leg which makes for some weird skins if they have asymmetrical leg textures. I've seen reports on this bug for the 1.16 beta but not for the official release of 1.16 so I just added this report just in case.