Hi,
I haven't played very many games yet so I'm not very knowledgeable. However I am wondering if you are playing as the Terran race and researched the Stellar Cartography tech? I certainly took note of it's description upon completion of it being researched.
"Our sensors allow us to see stars throughout the galaxy, but not necessarily planets. Those planets that we think are high quality may show up slightly different on our mini-map scanner now."
From that description of the Stellar Cartography tech I would also take it that planets that you might think are low quality might show up differently now too, as ah-em, higher quality.
I might be completely off base here but I thought I'd take a stab at why you're seeing what you are. Someone please correct me if I'm wrong in my assumption(from the description) about what Stellar Cartography does.
Regards