I just ran into a weird issue where one of my Agents is unable to submit a Change from the Change Catalog, but is able to submit it if he switches to the Portal view of the catalog. If I use a test account with the same role, I see the same issue.
The role has the following permissions for Changes and the Change catalog:

In the agent view, the Subcategory is missing from the ticket for him, and on Submit this error pops up after clicking Create:

Here's a screenshot of the missing subcategory:

And here's the same Change Catalog item viewed as an Administrator:

Note: We've only recently started using the Change Catalog, so there's a good chance I just have this misconfigured.