How to reproduce:

1. start a segmentation
2. paint a label
3. add an instance and paint
4. add a label and paint
5. add a label and paint -> color is off until first refresh

It seams to be always off by the number of instances (as it is forshadowing the color that will come)
I guess the reason is that some how the first color is picked soley based on the instance numbers. And then it is updated, but it is not directly propagated to the look up table of the mapper