I have a 'Complex Animation' set to move an object by 'Y Offset' with a value of '-300' and the animation works normally when the 'Amount' is set to '100'. If I manually set the 'Amount' to 50, then the object only moves '-150' when the animation plays, as expected.
When the 'Amount' is set by a variable or formula, the correct value is shown in the 'Text Preview' but the last-used manual value is shown in the animation editor. This prevents the animation from running the desired 'Amount'.
Screenshots:
http://i.imgur.com/Q0F9zWY.png
http://i.imgur.com/FJRS6sJ.png