Problem still exists in v2019 on Win2010. SU was installed as admin.
File with 400 components and 700 groups. Tried to create a new component from some edges+faces. Result: spinning wheel of death etc. After a few minutes manually killed SU using the TaskManager.
Should be easy to reproduce I guess and high on the to-do list imho.
Edit: first making a group of the entities and closing the Outliner before you convert the group into a component seems to work.