Operating system: Windows 10
Graphics card: GTX Geforce 770
(blender2.8, 2019-01-17 10:44)
When I try to animate shape keys, the value keeps snapping back to whatever the original keyframe was. Granted, I'm fairly new, so I can't tell whether this is a bug or a mistake on my end. I had the same issue with a previous build (Blender 2.8 2019-12-26 22:09). Doesn't matter whether or not the record button is enabled. The layer is unlocked (it let me edit the value to set the first keyframe).
To make it easier to explain, here's a video capture of the problem: https://youtu.be/mcGlZgx5Y1s