Short description of error
I have a scene with a single light and a mesh with an emission material. I've set up a driver for the emission value, driven by the light energy.
The light energy is keyframed and controlled with an fcurve.
However, once the driver is connected to the light's energy, the light energy freezes and becomes will not update at any point in the fcurve. Changing the fcurve keyframe values or running the animation doesn't work.
If I delete the driver, the light energy animates properly.
I can't for the life of me work out the cause or exact steps to recreate this bug, it appears either the material or the light is permanently corrupted in some way.
Even copying the objects to a new blend, they remain corrupted.
I've tried removing and creating new animation data for the light, I've tried deleting the driver and creating a new one.
Absolutely nothing works. It's seemingly impossible without creating a new light and emission material.
I can create a new light and emission material in the same scene and setup and the exact same driver however, and this works.
I spent hours trying to suss this one out.
Horrible, random bug :(
See attached a simplified blend file demonstrating the problem. Notice how the light value doesn't change between frames 0-100 which is animated, but on deleting the emission material's driver, it works.
Also note how the timeline playhead only updates the energy value immediately on loading the blend. Try saving the file with the playhead in different positions and notice how the energy value is different on load. Also try moving the keyframes, this updates the energy value too.
Edit: Interestingly, if instead of adding Single Properties and referring to them in the Expression textbox, I can refer to the light directly with python (ie, bpy.data.lights["Point"].energy) in the Expression textbox and it works perfectly. However I'm warned by Blender that it is considerably slower doing it this way.