If you try to use 3D or 2D interpolation with any segmentation plugin, the green contour is missing and as a consequence interpolation doesn't work at all.
Is this still valid? I couldn't reproduce this. However, I noticed that there is no contour for the 3D interpolation in the multi-label case (regardless of the classic segmentation plugin being open or not).
If not, I propose to close this task and open another one for a more specific description of current contour / interpolation bugs.
To clarify: The 2D- and 3D-Contour of the interpolation, using the classic segmentation plugin still works (2D contour in yellow, 3D contour in green).
But, as stated above, no contour is shown for the 2D- and 3D-Contour of the interpolation, using the multi-label segmentation.
We already removed the interpolation widgets from multi-label segmentation a while ago as they were never adapted to the plugin. I also tested to have both segmentation views open, use the multi-label segmentation, and use the interpolation of the segmentation. It works for the first label of any layer. Other labels simply are not considered as inpuit for the interpolation and are ignored.