Thanks for pointing this out - we've seen this off and on for many Chrome Beta versions since around 20 or so, but they always fix it before a stable Chrome is released. From that we have to assume that if a user isn't using a stable Chrome version, they are willing to accept unstable behavior.
From some brief analysis of the animations that are failing, I would note that our animations are using the GWT animation code - we don't re-implement the animation timing, but make use of the same code that is found in GWT itself. I would suspect then that this bug will be present in some other GWT animations, and that a fix must either be made in Chrome itself, or in GWT. While we might be able to help in producing such a patch for GWT, it might not be worth it if Chrome is going to keep changing how that animation code works.
Looks like this could be a bug related to this topic - the linked discussions of problems go back to May of this year, which seems to be about the time I started seeing reports of this breaking in Chrome from IRC. Indeed - the GWT Animation.update method is doing some bookkeeping to see if the animation ought to stop based on the value of the timestamp passed into the animation callback. This code is the same in GWT 2.4 and 2.5, as well as some other JS animation libraries.