and the website opens, what is in the address bar after the fact? Probably because your browser, when you omitted the "www" as part of the auto-search function automatically tried it when it received no response at 127.0.0.1.
If you instead point to an address that will actually answer the web page request, then your browser won't automatically try what it thinks you wanted.
I do this in my house and office to block unwanted websites... So I have a web service running on one of my internal servers set for all non-specified address headers to go to a "This page is blocked" page.
So using your example, I pointed imdb.com to 127.0.0.1 and when I tried imdb.com in my browser it was sent to www.imdb.com when 127.0.0.1 failed.
I then directed it to a valid web server internal address in instead and this time my test went to the "This page is blocked" address.
As long as the browser doesn't get any response it will try variations in it's own attempt to correct a possible typo and give you what it thought you wanted.
If you do not have this problem it must be because of something in my system... However, during my search online I had the thought that other people have this problem on Windows 7 too. A search query of "hosts "windows 7" ignored" in Google returns with many results... This is strange...
I tried a tab, two tabs, one space, two spaces, more spaces between 127.0.0.1 and the address ("imdb.com") in my HOSTS file and used ipconfig /flushdns command before hitting the GO button in the address bar, and restarted DNS client service each time to have a difference, there was no difference. I tried enabling/disabling Google DNS service for TCP/IPv4 of the wireless network I use to connect to internet, it did not help either. I tried Firefox, portable Firefox, IE 64 bit, IE 32 bit but none of them used my HOSTS file...