Comment 2 for bug 1760493

Another addition:
After applying any extension assigning new selection sets in the GUI is not possible anymore as mentioned. But: When looking into the XML-Editor, there appear (empty) extension sets, when clicking the plus symbol in the extension sets dockable dialog (on Save and Reload they will be also visible in the GUI). So maybe that's of interest to track the bug down that there is this discrepancy between the GUI and the file.