Using the Multilabel segmentation plugin view and the Fill / Erase tool, a label set image with multiple layers is not correctly handled.
If the Fill / Erase tool is used on any layer, the active label of the first layer is always used.

To reproduce:

1. Load an image, open the multilabel segmentation plugin view, create a new label set image
2. create a new label on the first layer (automatic popup dialog)
3. create another label on the first layer
4. create a new layer and create a third label on that layer
5. select a specific color for the third label
6. use the fill tool on the third label (second layer)

See how the image is filled with a green(?) color, not using the specific selected color.

This only works if the second label on the first layer was activated and then the layer was changed.
The reason is that the layers are not respected by the tool to the active label is the second label, which does not exist on the second layer.