A fix for this bug is available here: https://github.com/Alfred-Franz/MITK/tree/T28585-Included_inheritence (thanks to @kannberg!). However, I did not create a pull request yet because the plugin generator as used in tutorial step 9 should be completely replaced by the project template (see discussion in T27701). This means that tutorial step 9 will have to be completely revised, which would probably be quite a bit of work. But I think especially the example code for using a region grower in this tutorial step is worth to keep it.
How should we deal with this?