Description of problem: Cannot assign any use context created through the UI as the Root Category for the subsite Steps to Reproduce: 1. Create a use context in the backend 2. go to /admin/subsite/ 3. try to find the use context in Root Category drop-down list
The "Root category" drop-down is actually a list of Domains. You can create a new Domain by going to /admin/terms/. The new Domain will then appear in the drop-down.
NB, as discussed yesterday, this functionality isn't available on the staging / production servers yet. It will, however, be in the final build.