I had accidentally typed the wrong URL for my test system into MSIE6 one day and whenever I try to visit the same site, MSIE6's autocomplete feature would NOT let me change the URL. The wrong URL I first entered was local:7001/ when I meant localhost:7001/. Now, each time I try to enter localhost:7001/, MSIE6 would replace what I typed with local:7001/.
There's no way to delete that URL in the address (unlike Firefox, Shift-Delete doesn't work for MSIE6's address bar). So I used the Clear History feature in MSIE6 and blew away my history.
Then I found that auto-complete not longer had previously entered folder paths in Windows Explorer nor the name of programs in the Windows Run dialog. This is definitely unexpected and very annoying.