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).