Redirection URL aliases only work as expected as long as the cache isn't cleared.
Steps to reproduce:
- Open Advanced/Manage URL aliases for some content
- Add an URL alias; leave "Alias should redirect" checked
=> Open the URL alias in another browser window: Redirection works
- Empty the cache
=> Open the URL alias in another browser window: you won't get redirected; instead, the content is displayed on both URLs (the new alias as well as the generated one).