Upon uploading a custom skin to Minecraft Pocket Edition / MCPE, An error message stating: "That is not a minecraft skin, Silly!" Appears.

Even though it is a proper skin.

This issue appears to be only on MCPE, As other players have stated that they've been able to upload the same file on other devices just fine.

It does not remove the custom skin that is already in use, However uploading the same file makes the error message appear. (It does not unequip the previous skin, But does not change the skin either.)

All the pre-made skins / skinpacks work just fine.

I could not find a bug report about this on this website, But I found people having the same issue asking about it on other sites.

Notable occurrences:

When I have picked a skin to upload, It opens the game as if I switched between tabs. This causes Minecraft to reload then show the message.

The bug could be related to Minecraft closing whenever one accidentally taps the home-screen or tabs button, Where it closes the game and needs to reload.

After said message is removed, The page remains covered in a transparent shadow, Even when changing between the skin related tabs.