My MacBook is still doing it after all updates and it seems to get worse. It used to have a bad habit of logging onto one of my neighbour's network without me knowing - and frustratingly, his router seemed to work just fine! But even his is now dropping off.
It seems that the longer the router is on the list, the flakier it becomes.
You know, I sold my last MacBook for a very similar problem and now, a new laptop and a year later and the same dramas.