It is now possible to create a static (3D) or dynamic (4D) mask on a 4D image.
The segmentation tools / algorithms have different ways to create a segmentation, e.g.
some tools always take the first time steps (like Threshold for 3D seg on 4D image, while 4D image on 4D images is OK)
others end always with 3D segs (e.g. Otsu when making a 4D seg on a 4D image)
others don't allow to confirm (Threshold in multilabel images for 3D on 4D)
Some masks are created on all time steps but are only valid for the first time step.
We should discuss this here and create a consistent user experience.