Errors saving skins to launcher library

Saving skins to the skin library within the launcher produces these error messages: "Unable to save skin" and, when attempting to duplicate a skin added through the Minecraft website, "Unable to duplicate skin". This bug was encountered after I used NameMC to upload one of their hosted skins to the Skins page of the Minecraft website using the "Apply" button.

Outside of the launcher skin library, skins work perfectly fine.