I don't know what exactly the problem is as the provided information is not enough, but we recently discovered a problem with the Animation property in similar scenarios. Please check if you have enabled the animation and if the problem goes away after you remove the Animation property from your code. If this is the case, the fix should be ready with the BETA release next week.
If disabling the animation does not help, or your scenario is different, please provide a sample code that reproduces the problem so we can investigate further.
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