When I am trying to change my skin there is no possible way to do it. Once I try to choose a custom skin that has the classic arm style after another skin has the classic arm style, it shows the last skin that had the classic arm style and the skin that you try to change to appears on the skinny arm skin instead of both of them (skinny arms and classic arms). Mojang, if you could, please fix this issue.
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NEW BUG FOUND TODAY

Even if you DO to get it to work (aka, exiting and reenter Minecraft) the skin that you click on the classic arm skin that got overwritten by the other classic arm skin, it will overwrite the previous skin with the skin that you tried to turn it into the classic arm skin.
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So Mojang, if you could, PLEASE FIX THESE ISSUES. Bye!