During a test, I created hundreds of local users on the development server, and then granted relevant rights to them. However, after backing up the site collection and then restored it to the test server, some unexpected issue popped up.
On the test server, I deleted all "local users" manually from SharePoint (these users belong to the development server), then created new local windows users through script like below:
net user usr1 Password1234 /add
Then granted the rights to these users for the site collection.
stsadm -o adduser -url http://TestServer -userlogin "TestServer\usr1" -useremail "usr1@TestServer.com.au" -group "Approvers" -username "usr1 test"
Then I found none of those test user accounts work! After a couple of hours struggling, I deleted all users from SharePoint, then added the test users into SharePoint user group through web page -------- it works!
When checking the user details, I found "i:0#.w" was added to the user account name automatically
This issue did exist in beta version. Obviously it's not a bug but a feature now.