Volume undo does not set to fallback layer buckets again

[fm3]

Context

In volume annotation with fallback layer, undo button of the annotation view (not restore older version), creates gray patches.

Expected Behavior

The fallback layer data should be shown again in those locations

Current Behavior

The buckets previously annotated are empty (color data only is shown)

Steps to Reproduce the bug

Create volume annotation with fallback segmentation
Brush in an area with fallback segmentation
hit “undo”

Your Environment for bug

Firefox 86 on Ubuntu