Newest doesn't ways mean best. Softwares in development usually come full of bugs. I this case you've already found one of them.. When you reach a more advanced level of mapping and want to do terrain and rock walls you'll find it impossible to be done on 1.6.4 simply because you can't select multiple vertices.
I've always been a radiant 1.5 user. But I've been there, I also tried zero radiant and different versions of it. So much shortcut commands had changed + all those bugs. I just had to go back to 1.5
[12:25] <JohnnyEnglish> morning Nounou
[12:25] <JohnnyEnglish> wotcha doing?
[12:25] <Nounou> hello
[12:26] <Nounou> nothing much, i've nothing to do at work so
[12:26] <Nounou> modeling woman
[12:26] <JohnnyEnglish> woo
[12:26] <JohnnyEnglish> real women?
[12:26] <Nounou> realistic yes, on maya