I am unable to change skins while playing Minecraft

As the pictures and quick videos show, it doesn't let me change skins while playing Minecraft.

This is EXTREMELY frustrating, and I already have written an email to your offices but I was told that they cannot help me and that I should write here. It would be a shame if me and other fellow players stopped playing Minecraft because of a silly but very angering bug/glitch like this. I have provided quite a lot of evidence and a long explanation, so please get back to me as soon as possible. I am positive that many other players have had the same issue as me. My friends and I will be forever greatful if you could resolve this issue.