When a property (such as color, visibility, material attribute) is controlled by keyframes, changes made outside animation mode are overruled as soon as the animation is Previewed or the Timelineslider is moved. The idea is to warn the user via a popup dialog, similar to the one for animated Views.
Unfortunately a bug in RC1 (Bongo_20_Release_x64_English_20161215_2_6_8091.msi) made this dialog popup superfluously. It was fixed and Lars published a RC2