When on the server list, the correct version number (say, if you're on 1.6.4 and looking for a 1.7.X server.), it might display as a different version than needed, I noticed this as I started up 1.6.4 and was looking at the many 1.7.2 servers I had, and there was an X, of course, but beside it it displayed 1.3.
For the picture, look at the bottom server. I loaded up 1.3, but it didn't work, and it does in 1.7.2.