It's pretty well-known that the original Wii mode of the Wii U is heavily locked up behind tight doors from anything the Wii U does. Unlike the 3DS' implementation for original DS games, the Wii U doesn't track anything that you do when you're in the Wii mode of the system. Or does it?! In fact, it kind of does, in an altogether useless sort of way.
When you put an original Wii game into the Wii U disc drive, the menu actually displays an image of a disc with the "Wii" logo in the corner of the icon, though it doesn't actually display what software is on the disc. If you click the disc you're given a message that says it's Wii format software, and you can click the button it shows to launch Wii mode and boot the game.
The Wii U's Daily Log application doesn't keep any record of the time you spent in Wii mode, nor any indication of what you actually did while you were in there. But! You might be surprised to find out that the log does indeed record if the Wii mode was at least booted at all on a particular day, by way of a tiny line of text below the actual software entries. Note that it doesn't indicate anything other than that it was indeed launched—no times, number of boots, or anything else. But it is distinct per user, so it will only show up on the Daily Log of the actual signed-in Wii U user that loaded it up. Neat?!
Check back tomorrow for another shocking Wii U secret!