Operating system: Windows 10
Graphics card: Nvidia GeForce GTX 960m
Broken: (example: 2.80, edbf15d3c044, master, 2018-11-28, as found on the splash screen)
Short description of error
Lamp object does not change power between keyframes correctly.
Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).
Open blender -
Ensure Render mode is in EEVEE render.
Begin by selecting the Viewport shading mode to Render.
Click spot lamp object.
In side properties panel set lamp Power to 0 - Right click to create a keyframe.
In Keyframe playback panel, set to frame 30
In side properties panel set lamp Power to 100 - Right click to crate keyframe.
In Keyframe playback panel, play the animation.
Between keyframes 0 and 30 there is no difference in lighting.
Scrubbing between frames 0 and 30 produces the desired effect.