Broken: 2.80 9b80c70fc5b
Short description of error
The usual behaviour now when changing the values of a keyed value slider is that the sldier turns orange to indicate that the values don't match with the animation anymore. Afterwards they can be keyed or they will jump back to their keyed values once the current frame changes.
With some shapekeys this does not happen. Instead the value jumps back instantly when changed. Even with autokey the value will jump back when sliding, completely ignoring the value input.
In this file there is a cube and a plane. The plane has the above described bug. When changing the value of the keyed shapekeys this should be clear. The current cube or any new object likely will not have the bug but at some point the bug will appear.
I couldn't find out how or why.