stitched_terrain.png and stitched_items.png on desktop

When the game is launched with Minecraft.app, the game creates files on the desktop called stitched_items.png and stitched_terrain.png.

EDIT: this is happening also on my windows computer.

Note that this bug is specifically the fact that the files are being created on the Desktop, as opposed to somewhere in %appdata%\.minecraft or ~/Library/Application\ Support/minecraft.