Patrice, that is a solution I might be able to use. The problem I'm facing is greater in scale. What I want to do is move group layers out of a complex Layers tree on to the trunk. These layer groups might have multiple layers with random layer modes. All of the layer groups are 'Pass through 100% opacity'. It was working (the moving layers), but then this problem showed up, and I'm still confused about "Pass through" layer mode's role and behavior.
This is Pass through documentation on GIMP's website.
This is Pass through documentation on GIMP's website.