Google this.
"safari autofill not working with some websites"
Not much more to tell.
Bob
I've removed the keychain entry for autofill, doubled checked the Safari prefs, repaired permissions,checked/unchecked Private Browsing...Safari simply no longer "remembers" names/passwords in various web pages.
Any suggestions?
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic