I created a new custom field (text<255) and gave it a description. The field is restricted to a certain project. That project has a field configuration.
When I update the new field's description, the description in the field configuration is not updated.

I would expect that changing a custom field's description in Admin, Issues, Custom Fields would also change the description of the field in field configurations. Sometimes it does do so I think, but not all the time.

I've seen this in multiple versions of JIRA over the past two years.