Using the dataset provided with the module, I am able to load it, save the scene, and load the scene back with the multivolume correctly loaded. I cannot reproduce the issue reported.

Andriy, I have uploaded the dataset for you to test. I have sent you the link by email.

I was able to reproduce the problem with your data.

The short answer I cannot fix this.

Here's the long answer. Multivolume support modules use DWI IO mechanisms for storage. This means a multivolume is stored as a DWI volume in an NRRD file. As it turns out, if you attempt to save multi-component data, NRRD write function performs a series of checks to determine whether it is a DWI or not, and it does not treat the data as DWI unless it has more than 6 components (see Libs/vtkTeem/vtkNRRDWriter.cxx:88).

As a workaround, you can create duplicate dataframes so that the total number of frames is more than 6.

Hopefully in the future the IO mechanisms for multivolume will be revised to get rid of this constraint, but for now it is what it is.

With the rearchitecture of MultiVolume implementation, it no longer depends on DWI infrastructure, and there should be no constraint on minimum number of components allowed. Tested with 3 frames -- import, saving and reloading work without issues.

Closing resolved issues that have not been updated in more than 3 months