Is it a size issue? I thought the same thing had happened to me, but it was all small rocky planets. Less than 0.025 Earth Masses IIRC, but I'm at work just now. They went from UNEXPLORED to their name, and gave me the $$$, but they're obviously not EVEN going to show "Discovered By" There's one bang in the middle of occupied space that is on the tip of my tongue and easy to test (15 - 20 Ly from Lave I think)
This came up in Januaryish, and one person replied something like "it's because you don't understand how exploration works", so someone, somewhere knows da system!