Curves compressed from additive animations will not interpolate correctly if they have two keys in a row with the same value. The second key will be ignored, leading to the curve interpolating earlier than intended. See linked UDN for more information, and a potential fix.
The values printed to the screen will interpolate from 1 to 0 from the start instead of staying at 1 for about half a second.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-81950 in the post.