A couple simple www vs no-www questions

[Seascape]

I've already read the "Make domain.com point to www.domain.com" thread, no problem. I've decided to go with "no-www" URL's, and use the htaccess code that appears in the 2nd post of that thread. Again, no problem.

My root domain and addon WP domains all redirect as-is to "no-www" URL's without any mods needed to htaccess...

But I'm just curious... right now I can open 2 separate browser tabs for my (non WP, plain HTML) addon domains, type both "domain.com" and "www.domain.com" will both appear in each browser tab respectively. Why is that?


And the htaccess code I mentioned above will redirect the "www" name to the "no-www" URL?


And to prevent Google from penalizing that redirect, I need to go into Google's Webmaster Tools and put in the preferred "no-www" URL? TIA.

[Seascape]

And the htaccess code I mentioned above will redirect the "www" name to the "no-www" URL?


Yep ,it does


But I'm still curious as to WHY I could get both the www and non-www version to show before?