Same thing cannot be performed in stable 4.3.1, because transforms are not displayables, and nodes cannot be dropped under transforms in displayable mode. Instead, here is how to reproduce:

1. Load MRHead
2. Use Editor to create a few structures
3. Use Model maker to create models from the labels. Create two model hierarchies
4. Go to Data module, set it to ModelHierarchy mode
5. Drag&drop a created model into the other hierarchy.
   In the stable version, it works as expected. In the nightly (23484 for sure, but most probably others too) the dropped node becomes invalid (grays out and the icon disappears, sometimes the node itself disappears)