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.