Essentially, whenever you create a Behaviour with a description, it's description will be cleared as soon as you hit the "Save" button in the Behaviour's "Fields" configuration.
Steps to Reproduce (tested in Jira 7.13.0):
- Navigate to the Behaviours Administration page and create a new Behaviour with the name "Test Behaviour" and a description reading "This description is doomed to disappear"
- Click the "Fields" selection under the "Operations" section of the Behaviour you just created.
- Once to directed to the Edit Behaviour screen, hit the save button and navigate back to the Behaviour Administration page.
- Voila! The Behaviour's description has magically disappeared!