I am running CS4.1 and replicated your situation and found it to work perfectly as expected. If you aren’t running the latest 4.1 update – install it, AME has an update too – get that one also.
If you are running 4.1 I’d say reinstall.
Brightness and Contrast is the effect I am using – it works as expected, moving it trimming it on either end altering the type of animation.
If you are using Auto Contrast that might be causing problems.
– JB
Jon Barrie
aJBprods
http://www.jonbarrie.net