Before the June 30th preview version of slicer, my work flow was:
Start slicer. Load a segment (.seg.nrrd) and corresponding volume data (.nrrd). In the Segmentations module expand the ‘Export/import models and labelmaps’, select Export for operation and Labelmap for output type and create a new node. This would give me a labelmap with the same dimensions as the corresponding volume data with the label of 0 for any areas that there were no labels.
As of the June 30th preview, if I follow this same protocol the output is a labelmap that is cropped to only include the space immediately surrounding the labels, so a different dimension than the corresponding volume.
Murat did find a work around that if when I export the labelmap, under the advanced options I can choose a ‘reference volume’. When I do this I do export labelmaps with the same volumes as the original volumes.